Brainy Puzzles
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# Infosys Puzzles

Hello ,

This post will contain all the puzzles from Infosys recruitment process. I will post 1 puzzle each day and solution at the end of the day..
Please try to solve it and we can have discussion here in the post.
Infosys First Puzzle :-

There is a escalator and 2 persons move down it.A takes 50 steps and B takes 75 steps
while the escalator is moving down. Given that the time taken by A to take 1 step is equal to
time taken by B to take 3 steps. Find the no. of steps in the escalator while it is staionary.
No Takers π
Alright, Here is the solution to the first puzzle ( I dont know whether this is correct or not) -

Frooty
Infosys First Puzzle :-

There is a escalator and 2 persons move down it.A takes 50 steps and B takes 75 steps
while the escalator is moving down. Given that the time taken by A to take 1 step is equal to
time taken by B to take 3 steps. Find the no. of steps in the escalator while it is staionary.

If A takes 1 step in one second, then B takes 3 steps in one second. If A takes t1 seconds to
take 50 steps, then B takes 150 steps in t1 seconds.
For B, to take 150 steps he requires t1 seconds,
then to take 75 steps he requires t1/2 seconds.
So now, s1=50, t1 = t1 & s2=75, t2=t1/2
ans= (s1*t2 ~ s2*t1) / (t1 ~ t2) which gives 100.
so 100 steps is the answer
Second Puzzle :

If the digits of my present age are reversed then I get the age of my son.If 1 year ago my
age was twice as that of my son.Find my present age ?
Sagar07 • Sep 27, 2011
73..........
Thats correct .

Father's age = 73 and Son's age = 37
Third Puzzle :

There are 6561 balls out of them 1 is heavy.Find the minimum no. of times the balls have to be
weighed for finding out the heavy ball.
Sagar07 • Sep 28, 2011
I think its 8... bcoz if u divide the balls in three parts, set of 2187 balls will be compared with set of 2187 balls, which one is heavier contains the heavy ball... if both of them weigh same dat means 3rd set contains heavy ball... that is 1st compaeison..
similarly, 2nd comparison will be between set of 729 balls
3rd-243, 4th-81, 5th-27, 6th-9, 7th-3 n last will be between set of 1 ball.....
Sagar07
I think its 8... bcoz if u divide the balls in three parts, set of 2187 balls will be compared with set of 2187 balls, which one is heavier contains the heavy ball... if both of them weigh same dat means 3rd set contains heavy ball... that is 1st compaeison..
similarly, 2nd comparison will be between set of 729 balls
3rd-243, 4th-81, 5th-27, 6th-9, 7th-3 n last will be between set of 1 ball.....
Perfect
Fourth Puzzle :

If i walk with 30 miles/hr I reach 1 hour before and if I walk with 20 miles/hr i reach 1 hour late.Find the distance between 2 points and the exact time of reaching destination is 11 am then find the speed with which it walks.
born_star16 • Oct 3, 2011
Let original speed be v and time taken be t...

As distance between two points is constant,
30*(t-1)=20*(t+1)=v*t

hence, v=24 mile/hr
t=5 hrs

distance between two points is 120 miles
born_star16
Let original speed be v and time taken be t...

As distance between two points is constant,
30*(t-1)=20*(t+1)=v*t

hence, v=24 mile/hr
t=5 hrs

distance between two points is 120 miles
Thats Correct .
Fifth Puzzle : -

Next number in the series is 1 , 2 , 4 , 13 , 31 , 112 , ?
Come on guys . The above puzzle is not so tough. It was in Infosys paper. Please try to solve it
born_star16 • Oct 10, 2011
Frooty
Come on guys . The above puzzle is not so tough. It was in Infosys paper. Please try to solve it
Sixth Puzzle -

Shahrukh speaks truth only in the morning and lies in the afternoon, whereas Salman
speaks truth only in the afternoon. A says that B is Shahrukh. Is it morning or afternoon and
who is A - Shahrukh or Salman?
Sagar07 • Oct 11, 2011
I think its afternoon and A is salman...........

Sagar07

No number has digits more than 4. All of them are 1 , 2, 4, 8 , 16 , 32 , 64 converted to
numbers in base 5.
Sagar07
I think its afternoon and A is salman...........
Seventh Puzzle -

Sometime after 10:00 PM a murder took place. A witness claimed that the clock must
have stopped at the time of the shooting. It was later found that the position of both the
hands were the same but their positions had interchanged. Tell the time of the shooting
(both actual and claimed).
what wud b the answer ?
π²
Ankita Katdare • Oct 16, 2011
The time should be 00.50 am. π
can you please explain the solution to Fifth Puzzle : -

Next number in the series is 1 , 2 , 4 , 13 , 31 , 112 , ?
may be the time is 11:10 pm actual and claimed to be 1:55pm...
Frooty
Seventh Puzzle -

Sometime after 10:00 PM a murder took place. A witness claimed that the clock must
have stopped at the time of the shooting. It was later found that the position of both the
hands were the same but their positions had interchanged. Tell the time of the shooting
(both actual and claimed).
Let us assume that the time is some time soon after 10.00 pm. Because there is one more solution after that but before 12 midnight. What is needed is a situation where the hour hand is symmetric to the orientation of the minute hand.
The hour hand moves 0.5 degree/min while the minute hand moves 6 degrees/ minute. At 10 the hour hand is 60 degrees from 12 and the minute hand is at 12. Let us assume that the hour hand moves by x degrees. This requires 2x minutes. In 2x minutes the minute hand moves 12x degrees.
For symmetry 60 - x = 12x
13x = 60 from which x = 4.615
The time will be 9.23 minutes past 10.
With interchanged hands the time will be 1:50.8 AM
Ans:
Time of shooting = 11:54 PM
Claimed Time = 10:59 PM

SOLUTION ::

lets say
murder takes place at h2 : m2 , meaning h2 hrs and m2 minutes...
also let the claimed time be , h1 : m1
we know that angle swept by hr hand in 1 hr=30 degree
and angle swept by min hand in 1 min=6 degree
now as per question , the hr hand at one time will sweep same angle
with respect to standard 12 o clock position
as the minute hand from the other time ....
so we can get two eqns as ,
6 m1 = 30 h2 + (m2 / 2) ........................................(a)
6 m2 = 30 h1 + (m1 / 2) ........................................(b)

11(m1 + m2) = 60 (h1 + h2) .............................(c)

also, we get from (a) & (b) ,
13(m1 - m2) = 60(h2 - h1) .............................(d)

now if we take , h1 & h2 as 10 & 11 repectively ,
from (c) we have m1 + m2 = 114.54 ................(e)

if we take , h1 & h2 as 11 & 12 repectively ,
from (c) we have m1 + m2 = 120
for that m1 = m2 =60 ....which would correspond to same time on clock ....hence not possible as per question ,

if we take , h1 & h2 as 11 & 12 repectively ,
from (c) we have m1 + m2 > 120 , which is not possible ...
and so on ...
we cant take h1 and h2 less than 10 , as murder takes place after 10 pm...
so putting the values of h1 and h2 in (d),
we get
m1 - m2 =4.6153 ........................(f)
from (e) & (f) ,
m1= 59.577
m2=54.9623

hence the claimed time is 10 : 59.577
and the actual time of murder is 11 : 54.9623
Eighth Puzzle :

I bought a car with a peculiar 5 digit numbered licence plate which on reversing could
still be read. On reversing value is increased by 78633.Whats the original number if all
digits were different?
Frooty
Ans:
Time of shooting = 11:54 PM
Claimed Time = 10:59 PM
The angular position of the minute hand and the hour hand can have a mirror symmetry about the 12 o'Clock mark or the 11 o'Cock mark. The idea is that the person might claim that in the dim light he could not differentiate between the two hands. This can happen only if a mirror symmetry is present. The time will be 9.23 minutes past 10.
With interchanged hands the time will be 1:50.8 AM. This is also a valid solution.
Frooty
Eighth Puzzle :

I bought a car with a peculiar 5 digit numbered licence plate which on reversing could
still be read. On reversing value is increased by 78633.Whats the original number if all
digits were different?
What is meant by reversed? Mirror image left to right (18 become 81) or upside down (58 becomes 28)?
bioramani
What is meant by reversed? Mirror image left to right (18 become 81) or upside down (58 becomes 28)?

In this case upside down
Frooty
Eighth Puzzle :

I bought a car with a peculiar 5 digit numbered licence plate which on reversing could
still be read. On reversing value is increased by 78633.Whats the original number if all
digits were different?
is the number 18256
on reversing the number the new no. is 95281.
if the digits r written as seen on old digital calculators...
I spent a lot of time on this and ended up with too many theoretical blocks because of the condition that the reversed number has to be 78633 more than the original. It does not seem that any five digit number will meet all thew conditions.
I shall await for the answer.
*pushkar* • Feb 10, 2012
hey what types of puzzles are asked in infosys.? My friend told me to solve puzzles like sitting arrangement, sequential order etc from RS Aggarwal but you guys are sharing analytical puzzles :-/
Kaustubh Katdare • Feb 10, 2012
*pushkar*
hey what types of puzzles are asked in infosys.? My friend told me to solve puzzles like sitting arrangement, sequential order etc from RS Aggarwal but you guys are sharing analytical puzzles :-/
I'm not sure whether there have been any recent changes to the way Infy conducts tests. But they always asked analytical and logical questions. You should be good at solving puzzles.
Only 0 1 6 8 and 9 can be read upside down. So on rearranging these digits we get the answer as 10968.
Bionic • Feb 10, 2012
The whole thing is confusin, please define the meaning of reversing...
Is is reversing 285 to 582
or
revesing 9 to 6
please xplain i wanna solve this puzzle pls...
Bionic
The whole thing is confusin, please define the meaning of reversing...
Is is reversing 285 to 582
or
revesing 9 to 6
please xplain i wanna solve this puzzle pls...
Reversing 9 to 6!
Bionic • Feb 10, 2012
I think this is the answer....
The original number is, 10968

when reversed you get 89601,
And when you take the difference between the two group of numbers, you get the increased 78633.
Bionic
I think this is the answer....
The original number is, 10968

when reversed you get 89601,
And when you take the difference between the two group of numbers, you get the increased 78633.
Yes! π
akash.kasina • May 31, 2012
Frooty
Fourth Puzzle :

If i walk with 30 miles/hr I reach 1 hour before and if I walk with 20 miles/hr i reach 1 hour late.Find the distance between 2 points and the exact time of reaching destination is 11 am then find the speed with which it walks.
is the distance 120 miles????and the speed for reaching destination in exact time is 12miles/hr...is it correct???π¨
Anoop Kumar • Jun 1, 2012
akash.kasina
is the distance 120 miles????and the speed for reaching destination in exact time is 12miles/hr...is it correct???π¨
120 miles with 24 mph
akash.kasina • Jun 1, 2012
ianoop
120 miles with 24 mph
oh!!! niceπ
ankur8819 • Jun 15, 2012
This is from my personal experience. π
There is a jailer and three prisoners in a room.Also there are 5 hats 3 Black and 2 white.
Each prisoner was made to wear a hat and guess the color of hat he is wearing..Each prisoner can see other's hat but not his.If a prisoner guesses the color of his hat correctly he is released else he is put back in Jail.Prisoner 1 guesses it wrong,prisoner 2 is sent to Jail.Prisoner 3 is released.How did he know ?
Sagar07 • Jun 16, 2012
ankur8819
This is from my personal experience. π
There is a jailer and three prisoners in a room.Also there are 5 hats 3 Black and 2 white.
Each prisoner was made to wear a hat and guess the color of hat he is wearing..Each prisoner can see other's hat but not his.If a prisoner guesses the color of his hat correctly he is released else he is put back in Jail.Prisoner 1 guesses it wrong,prisoner 2 is sent to Jail.Prisoner 3 is released.How did he know ?
Ankur, This kind of puzzle has been already solved.... Watch the thread "Princess Puzzle" by AKD...
sowjitha • Jul 3, 2012
Frooty
Sagar07 • Jul 4, 2012
sowjitha
Consider, its morning, so if A is shahrukh then the statement has to be true, but it says B is shahrukh..
and if A is salman then the statement has to be wrong, so, B can't be shahrukh, that means A is not salman..

So, its afternoon...

now, if A is salman then statement is true so, B is shahrukh....

So, A is Salman.
sowjitha • Jul 5, 2012
Sagar07
Consider, its morning, so if A is shahrukh then the statement has to be true, but it says B is shahrukh..
and if A is salman then the statement has to be wrong, so, B can't be shahrukh, that means A is not salman..

So, its afternoon...

now, if A is salman then statement is true so, B is shahrukh....

So, A is Salman.
But it is not mentioned that the statement is true
nibhani • Jul 8, 2012
the
Frooty
Fourth Puzzle :

If i walk with 30 miles/hr I reach 1 hour before and if I walk with 20 miles/hr i reach 1 hour late.Find the distance between 2 points and the exact time of reaching destination is 11 am then find the speed with which it walks.
the distance between two points is 125 mills...and it will walk with the speed of 25 mills/hour.......
explantion-
let that person takes x hours to reach the exact place at exact time...if its speed is 30mills/hour then it will cover the same distance as when its speed will be 20miils/hour then the distance covered will be same ,let this distance is "d"....then
with 30mills/hour it will take (x-1) hour and with 20mills/hour it will take (x+1) hour and in both case distance will be same..so
30/(x-1) =20/(x+1)
x=5 hours
and speed will be for reaching at exact time because time is 11am which is between 10am for 30mills/hour and 12pm for 20mills/hour...
(30+20)/(2) =25 mills /hour
so distance will be
d=25*5=125mills/hour
am i right?