A store manager finds a stack of money totaling $1290--made up of twenties and fifties. There are 42 bills in all. How many twenty dollar bills are there?

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Answer 1 · 2015-10-17T23:10:23

Twenties = 27 bills
Fifties = 15 bills

twenties = a
fifties = b

$20 \cdot a + 50 \cdot b = 1290$ $20*a+50*b=1290$ (1)
$a + b = 42$ $a+b=42$ (2)

Multiplying (2) by 20:

$20 \cdot a + 50 \cdot b = 1290$ $20*a+50*b=1290$ (1)
$20 a + 20 b = 840$ $20a+20b=840$ (2)

Subtracting (1) - (2)

$30 b = 450$ $30b=450$

$b = \frac{450}{30} = 15$ $b=450/30=15$ fifties#

$a = 42 - 15 = 27 t w e n t i e s$ $a=42-15=27 twenties$