Helen earns $1,840 per month, after taxes. Of her monthly pay, 45% is for rent, 1/10 is for utilities, and 1/5th is for food. How much money does Helen have left after all these expenses?

If I did my math correctly, Helen would have $463 left after her expenses.

The first step is to find how much money 45% of $1840 is. When you multiply 0.45 by 1840 I got 825. So 45% of $1840 is $840.
Then I needed to find what 1/10 of $1840 is. 1/10 is equal to 10%, or 0.1. If you multiply 0.1 by 1840 you get 184. So 1/10 of $1840 is $184. 
1/5 is equal to 20%, or 0.2. Take 0.2 and multiply it by 1840 and get 368. So, 1/5 of $1840 is $368.
I then added all three numbers, 825, 184, and 368, toghter and got 1377.
So now we know that $1377 is used to pay for Helen's expenses.
The last step is to subtract 1377 from 1840 to get the final answer of 463.
So, Helen has $463 dollars left after all her expenses.