Dustin has only nickels and quarters in his piggy bank. he has 49 coins total for a combined value of $8.85. how many of each type of coin does he have?

Well obviously quarters equal 25 cents.  So you have to divide the 8.85 by 25 first.  That means he could have 35 quarters.  That least the rest as being dimes.  So find the remaining amount of the 8.85.  If you have 35 quarters that's $8.75.  And 8.85 minus 8.75 is 10 cents.  which would be 2 nickels.  That only adds up 37 coins.  So you break down one of the 25.  That would mean 5 more coins could be nickels.  Add 37 and 5 to get 42.   Do it again.  25 cents in nickels would be 5 more coins.  would be 46.  that would be missing 2 coins. But don't forget you're also subtracting from the 35 quarters. Now you would technically have 12 nickels and 33 quarters.  So you can do it one more time.  32 quarters means there is $8 in quarters at this point.

Now add you have 12 nickels, and you made 5 more.  That's 17 nickels.  That equals 85 cents.  So add 17 and 32 to be sure you have 49 coins, which you do. 

So 17 nickels, 32 quarters to equal 49 coins and $8.85

(sorry some of it got mixed up above because I was forgetting to subtract the quarters from the total as I changed them to nickels, so pay attention to the end)