You have a checking account with $500 in it. You deposit $300 on the same day that a check is processed from your account. Your new balance is $750. How much money was the check written for? $__

The check was written for $50.

Starting balance: $500
Deposit: +$300
New balance: $750

Therefore, the check amount must have been ($500 + $300) = $750.
So, the check was written for $750.