Question

You have a balance of $15,300 on your credit card with an 18% interest rate (1.5% per month). You pay $200 this month. Did your balance go up or down?
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Answer 1

If balance is positive you will get $229.5 additionally So total balance will go up.
If balance is negative you charged $229.5 and you will add $200. So total balance will go down.

Answer 2

Balance went up.  
First, calculate the interest that will accumulate for 1 month on your current balance.
 15300 * 0.015 = 229.5 
 Right now, we can stop since it's obvious that $229.50 of interest is greater than the $200.00 you're paying for that month. The new balance on your card will be:
 $15,300 + $229.50 - $200 = $15,329.50