n=number of nickles
d=number of dimes
p=number of pennies
so we have
"twice as many nickles as dimes"
n=2d
"five times as many pennies as dimes"
p=5d
we know that the total value is 200 cents
value=5n+10d+1p
200=5n+10d+p
we know that
n=2d
p=5d
sub those for n and p
200=5(2d)+10d+5d
200=10d+10d+5d
200=25d
divide both sides by 25
8=d
there are 8 dimes
easy, sub
n=2d
n=2(8)
n=16
16 nickles
p=5d
p=5(8)
P=40
40 pennies
40 pennies
16 nicles
8 dimes