It takes Ralph 12 hours to paint a fence alone. Lisa can do the same job in 15 hours. If Ralph paints alone for 40 minutes befor

Question

3 years ago

5

It takes Ralph 12 hours to paint a fence alone. Lisa can do the same job in 15 hours. If Ralph paints alone for 40 minutes befor

e Lisa begins helping, how long must they work together to finish painting the fence? Give your answer as a simplified fraction.

Mathematics

1 answer:

Aleks [24] · Answer 1 · 2022-05-07T01:03:43+03:00

After 40 minutes, Ralph has already painted (40/60)/12=1/18 of the fence

Lisa's speed is 1/15 fence/hour, Ralph's speed is 1/12 fence/hour, hence when they help each other their combined speed is 1/15+1/12=3/20

Thus we need to solve 3/20*x=17/18 thus x=170/27 hours (approx 6 hours 15 mins)