Pudge had 2.25 in dimes and nickles. if he had twice as many dimes as nickles. how many of each coin did he have

First, write an equation system based on the problem
For an instance, d stands for the number of dimes and n stands for the number of nickels. Dime's worth $0.10 and nickel's worth 0.05

"Pudge had 2.25 dimes and nickels" could be written as
⇒ 0.10d + 0.05n = 2.25  (1st equation)

"He had twice as many dimes as nickels" could be written as
⇒ d = n   (2nd equation)

Second, solve the equation system
Substitute d as n from the second equation to the first equation to find the number of nickels
0.10d + 0.05n = 2.25
0.10n + 0.05n = 2.25
0.15n = 2.25
n = 2.25/0.15
n = 15

Because d = n, therefore d = 15

Pudge has 15 coins of dimes and 15 coins of nickels