Barbara has D number of Dimes and however many N Nickels she has it is also equal to 2 x D so remember that. The total of coins multiplied by their value gives you the total amount of the money which is is 4.40 so 0.10D + 0.05N = 4.40.
You can't solve the equation with 2 unknown so if you can change the equation to 1 unknown that would work, well you can change the N unknown to a D because you know that N is also equal to 2 x D so substitute it.
(0.10)D + (0.05)(2D) = 4.40
.20D = 4.40
D = 22
That leaves 44 nickels. (0.10)(22) + (0.05)N = 4.40 <--Solving for N
You could have intuitively solved this by knowing that dimes, being worth twice nickels, had to cover half the amount of 4.40, which is 2.20 right? So that is 22 dimes, and twice that is 44 nickels covering the other 2.20.
But using the right algebra expression is the right way to go as the questions get harder and intuition won't come as easily....
All the best
Lori
