Ben had twice as many nickels as dimes. Altogether, ben had $4.20 how many nickels and how many dimes did Ben have

Dimes are worth twice as much as nickels, so all you have to do is divide it by half, which gives you 21 dimes, (2.10) and double that for the other half of nickels 42 (2.10) 2.10 + 2.10 = 4.20