Question 177161: Find two numbers whose sum is 39 and such that one is 2 times as large as the other. (We will call the two numbers x and y.) Answer by ptaylor(2198) (Show Source):
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Let x=one number
Then 39-x=the other number
Now we are told that one number (lets say x) is 2 times as large as the other, so our equatin to solve is:
x=2(39-x) get rid of parens
x=78-2x add 2x to each side
x+2x=78-2x+2x collect like terms
3x=78 divide each side by 3
x=26---------------------------one number
39-x=39-26=13---------------the other number
OK now we will call the two numbers x and y
x+y=39-------------------eq1
and
y=2x----------------eq2
substitute y=2x into eq1
x+2x=39
3x=39
x=13 one number
y=2x=2*13=26 the other number
