N + D = 15 (1)
5N + 10*D = 110 (2)
Multiply eq(1) by 5 (both sides). Keep the equation (2) as is. You will get
5N + 5*D = 75 (1')
5N + 10*D = 110 (2')
Subtract eq(1') from eq(2').
10D - 5D = 110 - 75
5D = 35
D = 35/5 = 7.
ANSWER. 7 dimes, and the rest of coins, 15 - 7 = 8 are nickels.
You will find there the lessons for all levels - from introductory to advanced,
and for all methods used - from one equation to two equations and even without equations.
A convenient place to quickly observe these lessons from a "bird flight height" (a top view) is the last lesson in the list.
Read them and become an expert in solution of coin problems.
