Question

William buys a book for $14.85. If he pays with a $20 bill, what will his change c be? Write an equation.

Answer 1

Answer:  14.85 + c = 20

============================================================

Reason:

To compute the change, we subtract the amount William gives the cashier (the $20) and the price of the book ($14.85)

The change c is

c = 20-14.85

To rearrange this equation, we can add 14.85 to both sides to end up with 14.85 + c = 20

In other words, solving that equation in bold leads to c = 20-14.85 = 5.15 which is the change William is given.

----------------

Extra info (optional section)

If the cashier wanted to mentally figure out the change in his/her head, then notice the jump from 85 cents to 100 cents is 15 cents. That means we go from 14.85 to 15.00

Then the jump from $15 to $20 is an extra 5 dollars. Overall, the total change given back to William is 0.15+5 = 5.15 dollars.