Scott wants to tip his tax icad driver 20%. Lf his commute costs $15 what is the total cost

20% in decimal form (and the form we need to do math with) is 20/100 or 0.20 (because there's 20 units for every cent; 20 for every hundred).

You multiply 15 (the total cost) by 0.20 to get 20% of 15, then add 15 to 20% of 15 to get the total cost.

0.2 (15) + 15 = 18

This works because you are multiplying 15 by one fifth of its value (20%) then adding the actual cost to it.