Question

How to solve the question

Answer 1

You have the equations set up correctly. I will use r and b as the variables to make it easier to follow.

12r + 8b = 70
20r + 12b = 110

First let's solve one of the equations for one of the variables.

12r = 70 - 8b

$r = \frac{70-8b}{12}$

Now plug that in for r in the second equation.

$20( \frac{70-8b}{12})+12b = 110$

Simplify

$20(70-8b)+144b=1320$

$1400-160b+144b=1320$

$-16b = -80$

b = 5 grams

Now plug 5 in for b in one of the original equations to find r.

12r + 8(5) = 70

12r  = 30

r = 2.5 grams

So the red marbles weigh 2.5 grams, and the blue marbles weigh 5 grams.