M4maths Previous Puzzles

16 Jan 2019 Population

The population of rodents in a house doubles every day. Every day 25 rodents are killed. How many rodents are there if after every four days, the number of rodents becomes same again?

OPtion

1) 20
2) 5
3) 15
4) 6
5) 24
6) 12
7) 25
8) 16
9) 8
10) None of these

Solution

1st day - x
2nd day - (2x-25)
3rd day - [2(2x-25)-25]
4th day - 2[2(2x-25)-25] - 25 = 8x - 7*25

After fourth day the value becomes equal to the first day so 8x - 7*25 = x
Solving, we get x = 25

Correct Option: 7 Best Solution (0)