Question

Working alone, it would take Shandra 45 minutes to mow the lawn. To mow the same lawn, also working alone, it would take Kelly 1 hour and 15 minutes. If they work together, the girls believe it will take them 1 hour to mow the lawn. Which best describes the reasonableness of their solution?

Answer 1

No! It would take them two hours. Seventy-five(an hour and fifteen minutes) plus sixty minutes would equals one thirty-five. Which is two hours.

Answer 2

Given: Shandra can do the complete work in 45 minutes.

So, Shandra's 1-minute work = 1 / 45  and

Kelly can do the same complete work in 1 hour and 15 minutes = 75 minutes.

So, Kelly's 1-minute work = 1 / 75

Now, we shall calculate Shandra's and Kelly's 1-minute work

By both 1 minute work = (1/45) + (1 / 75) = 8 / 225

∵ 8 /225 Parts can be completed by both = in 1 minute

∴ Complete work (1) can be completed by both = 225 / 8 minutes

or,                                                                           = in 28 minutes and 7.5 second

Hence, the assumption taken by both was incorrect.

The best described time will be 28 minutes and 8 seconds.