Represent the unknows with n and d.
Then n+d = 44 (# of coins)
and
$0.05n + $0.10d = $3.10 (value of coins)
Solving the first equation for n, we get n = 44-d. Subst. 44-d for n in the 2nd equation:
0.05(44-d) + 0.10d = 3.10
Then 2.20 - 0.05d + 0.10d = 3.10, or
2.20 + 0.05d = 3.10, or 0.05d = 0.90. Solving for d,
0.90
d = -------- = 18
0.05
There are 18 dimes and 44-18 nickels. How many nickels is that? ;)