if n = number of nickels and q = number of quarters, we have:
5n + 25q = 600
and
0.2q = n or q = n/0.2
Put this last back in to the first equation:
5n + n/0.2 = 600
5n + 5n = 600
10n = 600
n = 60
S0 there are 60 nickels and 12 quarters.
Check
$${\mathtt{60}}{\mathtt{\,\times\,}}{\mathtt{5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{12}}{\mathtt{\,\times\,}}{\mathtt{25}} = {\mathtt{600}}$$
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