Does not seem to be as easy as it looks?

Question

Emily and Jasper are working at a car wash. It takes Emily 20 minutes to wash a car by herself. Working together, Emily and Jasper wash a car in 12 minutes. Which equation can be used to find j, the number of minutes Jasper takes to wash a car by himself?

 

 

a)  12j=20

b)  12 + j = 20

c)  (1/20)+(1/j)=(1/12)

d)  (1/j) = (1/20) + (1/12)

 

Answer 1

Emily does 1/20 of the job per minute.

 

If it takes Jasper J minutes then he does 1/J part per minute

 

12(1/20 + 1/J) = 1

 

1/20 + 1/J = 1/12

 

Answer is C