One pump can empty a pool in 4 days, whereas a second pump can empty the pool in 10 days. how long will it take the two pumps, working together, to empty the pool? (fractional answers are ok.)

20/7 days (just less than 3 days)

Step-by-step explanation:

Recall that (1 job) = (rate)(time), so time = (1 job) / (rate).

Set up and solve the following equation:

  1 job

= time required for 2 pumps working together

1 job         1 job

+

4 days      10 days

This comes out to:

              1 job

= time required

10 job-days      4 job-days

+

   40 days           40 days

or:

    1 job

= (40/14) days, or 20/7 days (just less than 3 days)

14 job·days

   40 days  

whatever you can spend with $11.53 or under.

step-by-step explanation:

20 - 8.47 = 11.53. take away the money he used for lunch from the starting amount of 20.