Problema Solution
Lisa can shovel snow from her driveway in 35 minutes. Jim can do the same job in 45 minutes. How long will it take Lisa and Jim to shovel the driveway together?
Answer provided by our tutors
If Lisa can shovel in 45 minutes, she can do 1/45 in one minute.
If Jim can shovel in 35 minutes, he can do 1/35 in one minute.
if it takes them x minutes together, together they can do 1/x in one minute.
amount lisa can do in 1 minute + amount Jim can do in 1 minute = amount they do together in 1 minute
so
1/45 + 1/35 = 1/x
multiply both sides by 315x (the LCD) and get
7x + 9x = 315
16x = 315
x = 315/16
x ≈ 19.69 minutes.