# Digit problem

#### paulmdrdo

##### Active member
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
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
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 $y$.