Question

A herd of 100 cows have food for 30 days. If 20 more cows are added. How long will the food last

Answer 1

Answer:

This is an indirectly proportional relation, because the food will last less if the number of animals increases.

What we can do is a rule of three, as we know that the food lasts 30 days for 100 animals, and we want to know how many days does it last for 120:

30 days -- 100 cows

 x days -- 120 cows

As it's an inderect rule of three, x = $\frac{100*30}{120}$ = 25.

The food will last 25 days for them.