Question

If 7a+3b=20 and 3a+7b=10, what is a+b?

Answer 1

3

Explanation:

7a+3b=20

3a+7b=10

Substitution:

`\begin{bmatrix}3\cdot (20-3b)/(7)+7b=10\end{bmatrix}`

`a=(20-3\cdot (1)/(4))/(7)`

`a=(11)/(4),\:b=(1)/(4)`

11=4 + 1=4 = 12/4

12/4 = 3