Calvin has $8.80 in pennies and nickels. If there are twice as many nickels as pennies, how many pennies does Calvin have? How many nickels?

Let X = the number of pennies.

The number of nickels would be 2X

A penny is 0.01 and a nickel is 0.05

Now you have:

0.01x + 2 (0.05x) = 8.80

Simplify:

0.01x + 0.10x = 8.80

Combine like terms:

0.11x = 8.80

Divide both sides by 0.11:

x = 8.80 / 0.11

x = 80

Pennies = X = 80 total pennies.

Nickels = 2x = 2 * 80 = 160 nickels.