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jxharmon

Member

Registered: 2007-01-08

Posts: 104

confused again on word problem

one number is 12 more than another. the sum of the smaller number and twice the larger number is 39. find the larger number.
x-12=n
n+2(x)=39 am I on the right track?

jxharmon

Member

Registered: 2007-01-08

Posts: 104

Re: confused again on word problem

n+2x=39; 2x=39-n; x=39/2-n; and now I am lost what am I doin wrong?

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: confused again on word problem

You're told that the bigger number (x) is 12 bigger than the smaller number (n). You can use this to write x in terms of n.

After that, you can rewrite the equation n+2x = 39 in terms of n only, which will make it a lot simpler.

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Why did the vector cross the road?
It wanted to be normal.

pi man

Member

Registered: 2006-07-06

Posts: 251

Re: confused again on word problem

It doesn't matter whether you solve for x or for n first.   Once you find one value it's easy to solve for the other.   You have the following 2 equations:
n=x-12
n+2x=39

Substitute x-12 for n in the second equation:
x-12+2x=39
3x=51
x=17

Now solve for n:
n=x-12
n=17-12
n=5

For me, that was the easiest way to do it.   The approach you were taking was fine too:
n+2x=39
2x=39-n
x=(39-n)/2   

Now use this value for x and substitute into your other equation:  n = x-12

n=x-12
n=(39-n)/2 - 12
2n = 39-n -24    (multiply each side by 2 to get rid of the fractions)
3n = 15
n =5

Same answer, just not quite as easy.