Question 168521
lets call the number of pennies p, nickels n, and dimes d.

.01p+.05n+.1d=8.4---eq 1
d=2p-6--------------eq 2
d=n-----------------eq 3
:
lets plug in values from eq 2 and 3 into eq 1  remembering that n=d

.01p+.05(2p-6)+.1(2p-6)=8.4

.01p+.1p-.3+.2p-.6=8.4

.31p=9.3

{{{p=30}}}
d=2(30)-6=54
and since d=n
then the number of nickels is 54