Q) Julie has $3.10 in change in her pocket. If she has only 50 cent and 20 cent pieces and the total number of coins is 11, how many coins of each type does she have?

2 answers

50 f + 20 t = 310

f + t = 11 ... 20 f + 20 t = 220

subtracting equations (to eliminate t)

30 f = 90 ... f = 3

substitute back to find t
50x + 20y = 310
x + y = 11

multiply bottom equation by 20

50x + 20y = 310
20x + 20y = 220

substitute into 1st equation via elimination

30x = 90

x = 90 รท 30

x = 3

solve for y

3 + y = 11

y = 11 - 3

y = 8

Answer: 3 50c pieces and 8 20c pieces