please help me with this problem, cant seem to figure it out

cbmcbm · 2009-10-09 02:31:28

Mary can paint a house in 4 hours. John can paint same house in 6 hours. How long will it take them to paint the house if they are woking totogether?

Thanks

cbmcbm · 2009-10-09 05:53:03

This is what i have done. how much mary paints in an hr=1/4. how much john paints in an hr=1/6. If the total time it takes for both is X hours, then Mary takes X/4 and John X/6. Now, together---- X/4 + X/6. form an equation 1=X/4 + X/6
1=3X +2X
--------
12

12=5x, x=12/5, x =2.4 hrs. in minutes 4/5hrs =4/5 * 60 =24 minutes

so time its takes to do it together is 2hrs and 24 minutes.

this is the correct answer according to my answer sheet but I honestly cant seem to really realy understand the concepts here. Can some one please enligten me and let me know if my reasoning here is right. thanks

mathsyperson · 2009-10-09 06:49:06

Your equations are right, but I think you might be confusing yourself a bit.

You correctly say that Mary paints 1/4 of a house in an hour, and John paints 1/6 of one.
Then you define X to be the amount of time they both need to paint a house.

That means that in X hours, Mary paints X/4 of a house, and John paints X/6 of one.
Importantly, the terms X/4 and X/6 are portions of house, not hours.

So then together they paint X/4 + X/6 of a house, and we also know that they paint their whole house in that time so we get X/4 + X/6 = 1.
From there, solve the equation like you did to get the correct answer.

cbmcbm · 2009-10-09 13:39:05

thanks so much it all makes so much sense now. I appreciate your explanation

Math Is Fun Forum

#1 2009-10-09 02:31:28

please help me with this problem, cant seem to figure it out

#2 2009-10-09 05:53:03

Re: please help me with this problem, cant seem to figure it out

#3 2009-10-09 06:49:06

Re: please help me with this problem, cant seem to figure it out

#4 2009-10-09 13:39:05

Re: please help me with this problem, cant seem to figure it out

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