Rate of Work * Time = Part of Job

Question

It takes Phillip 9 hours to proof a chapter of Hawkes Learning Systems' Introductory Algebra book and it takes Mandy 2 hours. How long would it take them working together? (Round your answer to two decimal places).

Answer 1

(1/9 + 1/2)x = 1 (the time Phil and Mandy finish per hour times the number of hours equals 1 book)

 

Step one -- LCD. 18 is the lowest:

(2/18 + 9/18)x = 1

11/18 * x = 1

 

Next -- isolate x:

x = 18/11

x = 1 7/11

 

Finally -- turn the fraction into a decimal:

7 ÷ 11 = .636363636363...

x = 1.64