Mrs Chan has twice as many $5 notes as $10 notes and twice as many $10 notes as $50 notes. She has a total of $1080. How many $10 notes does she have?

1 answer

number of 50's ---- x
number of 10's ---- 2x
number of 5's ----- 2(2x) = 4x

Now, consider the value of those notes to form your equation.

50x + 10(2x) + 5(4x) = 1080
50x + 20x + 20x = 1080
90x = 1080
x = 12

we defined 10's as 2x
so she has 2(12) or 24 $10 bills

check:
fifties 12
tens 24
fives 48

12(50) + 24(10) + 48(5) = 1080
YUP!!