SOLUTION: 30 coins total. Made up by only nickels and dimes. Total is $2.10. How many dimes and nickels?

Question 271339: 30 coins total. Made up by only nickels and dimes. Total is $2.10. How many dimes and nickels?
Found 2 solutions by checkley77, josmiceli:
Answer by checkley77(12844) (Show Source): You can put this solution on YOUR website!
N+D=30
N=30-D
.05N+.10D=2.10
.05(30-D)+.10D=2.10
1.5-.05D+.10D=2.10
.05D=2.10-1.50
.05D=.60
D=.60/.05
D=12 NUMBER OF DIMES.
N=30-12
N=18 NUMBER OF NICKELS.
PROOF:
.05*18+.10*12=2.10
.90+1.20=2.10
2.10=2.10
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = number of nickels
Let = number of dimes
given:
(1)
(2) (in cents)
-----------------------------------
Multiply both sides of (1) by
and subtract from (2)
(2)
(1)

and, since

There are 18 nickels and 12 dimes
check:
(2)

OK

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