Let's say I work in a store and a costmer walks up to me and asks me how much are a pair of head phones. And I say $3.80. Let's say the custumer gave me $5.00. How much change will I give back to the custumr?

Subtract $3.80 from $5.00

5.00
- 3.80
____________

$1.20. The cent has to be rounded to the nearest dollar right? so I would add .80+.20=$1.00 right?

With money, we don't round to the nearest dollar. We round to the nearest penny. You should give $1.20 in change to the customer.

$1.20. $3.80 is almost $4.00 right? So that means I would give my custumer $1 and something right? Because the custumer already used his extra dollar right? And I got the .20 by rounding to the next dollar. So .80+.20=$1.00. So that's how I got $1.20.

Can I also work it out the way I just explained it?

Yeah. "The nearest penny" that's what I meant. Thanks. But is the way I describe it correct?

To determine the change to give back to the customer, you need to subtract the amount paid by the customer from the price of the headphones. Here's how you can do it step by step:

1. Start by figuring out the price of the headphones. Let's say a pair of headphones costs $3.80.
2. Calculate the change by subtracting the amount paid by the customer from the price of the headphones. In this case, subtract $3.80 from $5.00.
Change = Amount Paid - Price of Headphones
Change = $5.00 - $3.80
Change = $1.20
3. The change you need to give back to the customer is $1.20.

So, you would give back $1.20 in change to the customer.