A bag contains white marbles and green marbles, 59 in total. The number of white marbles is 7 more than 3 times the number of green marbles. How many white marbles are there?

Answer 1

w+g=59

w=7+3g

Two equations, two unknowns. I am showing several ways.

Elimination:

w+g=59

(w-3g=7)*-1 = -w+3g=-7

w+g=59

-w+3g=-7

Add them, 4g=52; g=13; w=46

Substitute (solving for w):

w+g=59

w=7+3g

7+3g+g=59; 7+4g=59; 4g=52, g=13; w=46