# Maria can build a model train in 7 hours. Anne can build a model train in 5 hours. How long would it take them if they work together?

##### 1 Answer

#### Answer:

They would need **2 hours** and **55 minutes**.

#### Explanation:

The key to this problem is to figure out how much of the complete train the two girls can each build *per hour*, assuming of course that they work at a constant rate.

This will give you an idea about how much of the train they can build *together* per hour.

So, if Maria can build a complete train in **7 hours**, then she needs **1 hour** to complete

Likewise, Anne can build a complete train in **5 hours**, so she needs **1 hour** to complete

This means that , **together**, they can complete

To determine how many hours they need to complete the train, find a number that multiplied with

To express this in hours, use the fact that one hour has **60 minutes**

The total time will thus be