Mrs Reggie had a sum of money. If she bought 5 chocolate bars and 6 mochi balls, she would have $48 left. If she bought 3 chocolate bars and 9 mochi balls, she would have $50 left. Given that she had $80, how many chocolate bars could she buy at most?
Cost of 1 chocolate bar = 1 C
Cost of 1 mochi ball = 1 M

5 C + 6 M + 48 = 80
5 C + 6 M = 80 - 48
5 C + 6 M = 32 ---- (1)

3 C + 9 M + 50 = 80
3 C + 9 M = 80 - 50 
3 C + 9 M = 30 ---- (2)

Make M the same.

(1) _{x 3}
15 C + 18 M = 96 ---- (3)

(2) _{x 2}
6 C + 18 M = 60 ---- (4)

(3) - (4) 
15 C - 6 C = 96 - 60
9 C = 36

1 C = 36 ÷ 9 = 4

Number of chocolate bars that Mrs Reggie can buy
= 80 ÷ 4
= 20 r 0

Most number of chocolate bars that Mrs Reggie can buy = 20

Answer(s): 20