Introduction:
Puzzles are dealt in a detailed manner with certain solutions.
Different puzzles are gathered from Shakuntala Devi puzzle
books. Keeping in mind certain puzzles for Infosys some
reasoning problems are also dealt. Puzzle name at the top of
each problem will give a brief idea regarding the mode of
application.
SELECTING A CANDIDATE
For an advertisement of six local posts,twelve persons applied
for the job.Can you tell in how many different ways the
selection can be made?
Solution:
6^12
SET OF BAT AND BALL
When I wanted to buy a bat and ball, the shopkeeper said they
would together cost Rs.3.75.But I did not want to buy a ball.
The shopkeeper said that bat would cost 75 paise more than the
ball.What was the cost of bat and the ball?
Solution:
Given that bat and ball together cost Rs.3.75 = 75 paise
Let cost of the ball alone be x.
Given cost of the bat is 75p greater than cost of the ball.
So cost of the bat = x+75
x+x+75 = 375
2x = 375 - 75
2x = 300
x = 150p
Hence cost of the ball = Rs.1.50
=>Cost of the bat = 1.50 + 75 = Rs.2.25
PLAYING CHILDREN
A group of boys and girls are playing.15 boys leave.There remain
2 girls for each boy.Then 45 girls leave.There remain 5 boys for
each girl.How many boys were in the original group?
Solution:
Let B and G represent no.of boys and girls in the original group
respectively.
G ---------> 2
B-15 ----------> 1
G/B-15 = 2/1
i.e., 2 girls are left for 15 boys who are alone.
G-45 -------------------->1
B-15 ------------------------->5
5 boys are left out when 15 girls are alone.
=>G/B-15=2/1 --------------------------------(1)
=>G-45/B-15 =1/5 ----------------------------(2)
(1) & (2) =>
G = 2B-30
5G - 225 = B - 15
5 ( 2B - 30 ) = B - 15 + 225
10B = B - 15 + 225 + 150
9B = 360
B = 40
(1)=> G/40-15 = 2
G=50 girls.
Problems
1.Reshma appeared for a maths exam.She was given 100 problems to
solve.She tried to solve all of them correctly but some went
wrong.But she scored 85. Her score was calculated by subtracting
two times th no.of wrong answers from the no.of correct answers.
How many problems did Reshma do correctly?
Solution:
Assume W as wrong answers and R as correct answers
Given total no.of questions as 100
R+W=100 ---------------------------(1)
Score is calculated by subtracting 2 times wrong answers(2W)
from right answers(R) and given as 85
R-2W=85 -------------------------------(2)
(2)-(1)
R-2W=85
R+W=100
---------------------
W=5
Hence,100-5=95 is the no.of correct answers of Reshma.
2.A RUNNING RACE
Sneha, Shilpa, Sushma join a running race.The distance is 1500 Meter.
Sneha beats Shilpa by 30 Meter and Sushma by 100 Meter. By how much could Shilpa beat Sushma over the full distance if they both ran as before?
Solution:
Total distance covered by Sneha=1500m
Shilpa=1500-30=1470
Sneha =1500-100=1400
Distance covered by Shilpa=1500*1400/1470=1428.6
Distance to be covered by Shilpa to beat Sushma over full distance
1500-1428.6=71.4m
3.FILLING A CISTERN
Pipe S1 can fill a cistern in 2 hours and pipe S2 in 3 hours.Pipe S3
can empty it in 5 hours.Supposing all the pipes are turned on when
the cistern is completely empty,how long will it take to fill?
Solution:
S1 fills cistern in 1/2 hours
S2 fills cistern in 1/3 hours
S3 empties it in 1/5 hours
A the pipes S1,S2,S3 working i.e.,filling the cistern
1/2+1/3-1/5=15+10-6/30=25-6/30=19/30
No.of hours to fill=30/19=1 11\19 hours.
4.SEQUENCE PROBLEMS
What are the next two terms in the sequence?1,1,5,17,61,217.........
Solution:
The order in this cases is
Tn=3*Tn-1 +2*Tn-2
= 3(217)+2(61)
= 773
Tn+1=3(773)+2(271)
=2319+542
=2753
5.SEQUENCES
What are the next two terms in the sequence?
1,1,5,17,61,217.................
Solution:
Tn=3Tn-1+2Tn-2
