Question

Kyla can plant 300 trees in 1 hour

Answer 1

We have to find out the number of trees planted per unit rate of time.

Kyla can plant 300 trees in 1 hour, so she can plant 300 trees in 3600 seconds. This implies that she can plant

$\dfrac{300}{3600}=\dfrac{1}{12}$

trees per second.

On the other hand, Mia can plant 1 tree in 13 seconds, so she can plant

$\dfrac{1}{13}$

trees per second.

Working together they can plant

$\dfrac{1}{12}+\dfrac{1}{13}=\dfrac{25}{156}$

trees per second, i.e. it takes them 156/25 seconds to plant a tree.

We conclude that they plany 100 trees in

$\dfrac{156}{25}\cdot 100=156\cdot 4=624$

seconds