Only 30 of Jahanna's 40 customers receive the newspaper on Sunday's. If it takes her 50 minutes to deliver to 40 customers on other days, how long will it take her to deliver the paper to 30 customers?

37.5 minutes

Step-by-step explanation:

It takes Jahanna 50 minutes to deliver to 40 customers.

On Sunday however, she has to deliver to only 30 customers.

Assume that the amount of time it will take her is x minutes and use direct proportion:

50 minutes          :       40 customers

x minutes             :       30 customers

Cross multiply:

40x = 50 * 30

40x = 1,500

x = 1,500/40

x = 37.5 minutes

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.