7th Grade Challenging Math
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7-45)
Answer
5 days
Solution:
The amount of grass that 10 sheep eat
in 20 days = original amount of grass + new growth in 20 days
The amount of grass that 15 sheep eat in 10 days = original amount of grass +
new growth in 10 days
Assume the amount of grass one sheep
eats in one day is 1. Therefore,
The amount of grass
10 sheep eat in 20 days = 1 x 10 x 20 = 200
The amount of grass
15 sheep eat in 10 days = 1 x 15 x 10 = 150
The amount of grass that grows in 10 days is
200-150 = 50
The amount of grass that grows in one day is 50/10 = 5,
which can feed 5 sheep for one day;
Therefore the original amount of grass is 200 - 5 X 20 =100
Since new grass grows in one
day can feed 5
sheep, the original grass only needs to feed 20 sheep. (25 -
5 = 20)
Therefore, 25 sheep can feed on the land for 100/(25 - 5)
= 5 days
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