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)   (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

 

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