A man has a combination of $\$5$ and $\$10$ notes. If the total number of notes is 20, and the total value of money is $\$120$, what is the quantity of $\$10$ notes?
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A man has a combination of $5 and $10 notes.
If the total number of notes is 20, and the total value
of money $120, what is the quantity of $10 notes?
Call F the number of fivers
Call T the number of ten-spots
F + T = 20 ——>> F = 20 – T (equation 1)
5F + 10T = 120 (equation 2)
Substitute (20 – T) in place of F in (equation 2).
(5)(20 – T) + 10T = 120
100 – 5T + 10T = 120
5T = 20
T = 4 This is the number of ten-dollar notes, which also
means there are F = 20 – 4 = 16 five-dollar notes.
We'll use the number of five-dollar notes later.
check answer
(eq 1) 16 + 4 =? 20
20 = 20
(eq 2) (5 • 16) + (10 • 4) =? 120
80 + 40 =? 120
120 = 120
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