Jimmy collects nickels and dimes. Right now, he has a total of 40 coins in his piggy bank. If there are seven times as many dimes as there are nickels, how many nickels does Jimmy have?

Number of nickels plus number of dimes equals total number of coins

so

n + d = 40

then they tell us that "there are seven times as many dimes as there are nickels"

this translates to

d = 7n

we then plug that into our first equation

and get

n + 7n = 40

then we solve for n

add like terms

8n = 40

then divide both sides by 8

n = 40/8 = 5

therefore Jimmy has 5 nickels