Question

It takes a boy 30 minutes to mow the lawn, but his sister can mow it in 45 minutes. how long would it take them to mow the lawn if they worked together, using two lawn mowers?

Answer 1

`\text{The boy can mow the lawn in 30 minutes,}\\ \text{so in 1 minute he can mow the lawn}=(1)/(30)\text{ part}\\ \\ \text{And his sister can mow the lawn in 45 minutes,}\\ \text{so in 1 minute she can mow}=(1)/(45) \text{ part}\\ \\ \text{so if they work together, in 1 minute they can mow}\\ \\ =(1)/(30)+(1)/(45)`

`=(3+2)/(90)\\ \\ =(5)/(90)\\ \\ =(1)/(18)\\ \\ \text{since in 1 mintute together they can mow}=(1)/(18)\text{ part},\\ \\ \text{so they together will mow the lawn in}=18 \text{ minutes}`

Hence they together will mow the lawn in 18 minutes