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Digit problem

paulmdrdo

Active member
May 13, 2013
386
can you help me solve this just using one variable

the sum of two numbers is 9 and their difference is 6. what are the numbers?

thanks!
 

Evgeny.Makarov

Well-known member
MHB Math Scholar
Jan 30, 2012
2,492
the sum of two numbers is 9 and their difference is 6. what are the numbers?
Let $x$ be the smaller of the two numbers. Since the difference is 6, the other number is $x+6$. Now try writing the equation saying that the sum of these numbers is 9 and try solving it.
 

Deveno

Well-known member
MHB Math Scholar
Feb 15, 2012
1,967
Alternatively:

$x + y = 9$
$x - y = 6$

The second equation tells us:

$x = y + 6$

So substitute that value for $x$ into the first equation, to get an equation in the single variable $y$.