A person has 17 coins, all nickels and dimes, worth $1.25. How many nickels are there?

This is a problem of guess and check; there's no easier way to do it. But in this case you must have an odd number of nickels to make the 5 cents, so your answer is 9 nickels. you can check this by multiplying each one by. 05: 9*.05=.45 the rest of the coins left, are 8 of them, and their dimes ...10*8=.80.80+.45 = 1.25