A collection of 70 coins consisting of dimes, quarters, and half dollars has a value $17.75. There are three times as many quarters as dimes. Find the number of each kind of coin.
Let h, q, and d denote the number of half-dollars, quarters and dimes.
Then what you are told is:
h + q + d = 70,
50*h + 25*q + 10*d = 1775
and:
q = 3*d
Substitute the last of these into the first two which will give you a pair
of simultaneous equations in two variables which you then need to solve.
The attachment shows QuickMath's solution
RonL