A student must leave for campus in 10 minutes or he will be late for class. Unfortunately, he is snowed in. He can shovel the driveway in 18 minutes, and his brother claims to be able to do it in 12 minutes. If they shovel together, how long will it take to clear the driveway? Will this give him enough time for the student to get to the campus?

Question

It will take about ? minutes to clear the driveway together. (type the integer or decimal rounded to one decimal place as needed)

Answer 1

If we consider the act of shovelling the driveway as 1 unit , then
his rate = 1/18 units/min
brother's rate = 1/12

combined rate = 1/18 + 1/12 = 5/36

time at the combined rate = 1/(5/36)
= 36/5 minutes
= 7.2 minutes

Answer 2

7.9 is the correct answer