3. if a home buyer puts 20% down on a $200,000 house and uses a mortgage to borrow the rest, how much will the mortgage be (excluding any closing costs)? $160,000

When the home buyer gives the downpayment, that could be calcualted this way:

$200000(0.2) = $40000

The rest would be for the mortgage. So, just subtract the downpayment from the original purchase price

$200,000 - $40000 =$160,000

Thus, the answer is $160,000. 

I hope I was able to help you. Have a good day.