Ms. Spinoni can prepare a mass-mailing of 500 letters in 10 hours. Mr. Harris can prepare a mass-mailing of 500 letters in 15 hours. How long will it take them to prepare a mass-mailing of 1000 letters if they work together? (Hint: The complete job is twice as big)

Question

a. 6 hours c. 12.5 hours

b. 12 hours d. 25 hours

Answer 1

Hmmm.

In 30 hours, they could make 500*3+500^2 or 2500 letters.

they have a joint rate of 2500letter/30 hours , which is 83 letters per hour (about).

time=1000/rate=1000/(2500/30)=30000/2500=12 hours