SOLUTION: Chris can mow the lawn in 20 minutes. His mother can mow the lawn in 30 minutes. Chris works for 10 minutes before his mother begins to help. How long do they work together to comp

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Question 1198720: Chris can mow the lawn in 20 minutes. His mother can mow the lawn in 30 minutes. Chris works for 10 minutes before his mother begins to help. How long do they work together to complete the job?
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
Chris rate, 1%2F20
Mother rate, 1%2F30
x, time while both are mowing
1, how many jobs, "MOW THE LAWN"

%281%2F20%2910%2B%281%2F20%2B1%2F30%29x=1
Simplify and solve.

Answer by ikleyn(52775) About Me  (Show Source):
You can put this solution on YOUR website!
.

In order for the mother could help, they should have two mowers.