SOLUTION: Please help me solve this! "Erica could do 10 math problems in 20 minutes. Penny could do 15 math problems in 25 minutes. If they worked together, how many minutes would it take

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Question 450613: Please help me solve this!
"Erica could do 10 math problems in 20 minutes. Penny could do 15 math problems in 25 minutes. If they worked together, how many minutes would it take Erica and Penny to do 30 math problems?"
Thanks and have a great day!
Found 2 solutions by ewatrrr, rwm:
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

"Erica could do 10 math problems in 20 minutes OR 10/20 = .5 in 1 min

Penny could do 15 math problems in 25 minutes OR 15/25 = .6 in  1 min

If they worked together... 

how many minutes would it take Erica and Penny to do 30 math problems?"

Let x represent the amount of minutes

 .5x + .6x = 30

       1.1x = 30

          x = 30/1.1 =  27.2727 minutes

Answer by rwm(914) About Me  (Show Source):
You can put this solution on YOUR website!
Erica can do one math problems in two minutes and .5 in 1 minute
Penny can do 15/25 in one minute
Another way look at it
Erica can do 30 problems in 60 minutes
So Erica can do the whole job in 60 minutes
Penny can do 30 problems in 50 minutes
Penny can do the whole job in 50 minutes
x/50+x/60=1
x/5+x/6=10
6x+5x=300
11x=300
x=300/11
x=27.27 minutes