Question

The sum of two numbers is 15, and their difference is 3. What are the numbers?

Answer 1

\[
a+b=15\\
a-b=3
\]

Answer 2

Adding both equations gets you: \[
2a = 18 \implies a=9
\]

Answer 3

\[
9+b=15 \implies b=6
\]

Answer 4

Sure enough\[
9+6=15\\
9-6 = 3
\]

Answer 5

you write two equations and solve for y, then substitute the answer into the second equation!
x + y = 15, x-y = 3
y = 15-x
x - (15-x) = 3
x - 15 + x = 3
2x - 15 = 3
x = 9
15-9 = 6

Answer 6

whoops nvm LOl too late xD

Answer 7

thank you all :D

Answer 8

\[\left[\begin{array}{cc|c}1&1&15\\1&-1&3\end{array}\right]\]\[\sim\left[\begin{array}{cc|c}1&1&15\\0&-2&-12\end{array}\right]\qquad R_2\to R_2-R_1\]\[\sim\left[\begin{array}{cc|c}1&1&15\\0&1&6\end{array}\right]\qquad R_2\to R_2/-2\]\[\sim\left[\begin{array}{cc|c}1&0&9\\0&1&6\end{array}\right]\qquad R_1\to R_1-R_2\]