The answer would be 10 dimes, 30 nickels and 50 pennies.
Step by Step
10 x 10=100
10 × 3=30
30×5=150
10×5=50
100+150+50=300
First you test out all the possibilities that the amount of dimes could be. When you choose a number you multiply that number by 3 since there are 3 times as many nickels as dimes, then you would multiply that number by 5. Lastly you would multiply the number of dimes by 5 because there are 5 times as many pennies as dimes. Eventually you would get the answers 10, 30, and 50.