Answer:First, you want to solve for the equation for this problem, would be:
0.05N + 0.10D = 20.50
While N = The amount of nickels, and D = The amount of dimes.
Since N = 164, and D = 123. It would add up to 287 coins. 164 + 123 = 287.
Now that you have the number for those two variables, solve the equation for when N = 164, and D = 123.
0.05N + 0.10D = 20.50
0.05(164) + 0.10(123) = 20.50
8.2 + 12.3 = 20.50
20.50 = 20.50
So, there is 164 nickels, and 123 dimes for your answer.
I hope this helps you