Aptitude Hack#1(24-2-19)

Question:

1)There are 25 horses among which you need to find out the fastest 3 horses. You can conduct race among at most 5 to find out their relative speed. At no point, you can find out the actual speed of the horse in a race. Find out how many races are required to get the top 3 horses.

A) 5

B) 6 

C) 7

D) 8   

Answer:  C)7

Explanation:

First make a group of 5 horses in one race So 5x5=25, no of races=5.
Name them as a1,a2….  b1,b2……. c1,c2….. d1,d2… e1,e2……..
Where a,b,c,d,e denoted group name and no represent their rank
Now take top horses from every group a1,b1…e1  and make a race =>no of race=6.
suppose result is a1>b1>c1>d1>e1 which implies a1 must be FIRST. b1 and c1 MAYBE 2nd and 3rd.
Now FOR 2^nd position,horse will be either b1 or a2 and For 3^th postion,horse will be either b1,a2,a3,b2,c1, no of race=7 

The final result will give ANSWER. suppoose result is a2>a3>b1>c1>b2 then answer is a1,a2,a3,b1,c1. HENCE ANSWER is 7 RACES.