Question 959228
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D=dimes; N=nickels
D+N=20
D=20-N
$0.10D+$0.05N=$1.40 Substitute for D
$0.10(20-N)+$0.05N=$1.40
$2.00-$0.10N+$0.05N=$1.40 Subtract $2.00 from each side.
-$0.05N=-$0.60 Divide each side by $0.05
N=12 ANSWER 1: There are 12 nickels
D=20-N=20-12=8 ANSWER 2: There are 8 dimes.  
CHECK:
$0.10D+$0.05N=$1.40
$0.10(8)+$0.05(12)=$1.40
$0.80+$0.60=$1.40
$1.40=$1.40