Question

A farmer has enough food to feed 20 animals in his cattle for 6 days. How long would the food last if there were 10 more animals in his cattle?

Answer 1

Let the number of days that the food will last if there were 10 more animals in the cattle be x. 
The following table is obtained.

Number of animals	20	20 + 10 = 30
Number of days	6	x

More the number of animals, lesser will be the number of days for which the food will last. 
Hence, the number of days the food will last and the number of animals are inversely proportional to each other. 
Therefore, \(20 × 6 = 30 × x\)
\(x=\frac{20 × 6 }{ 30}\)
Thus, the food will last for 4 days.