This is a complete lesson for learning how to add and subtract using percents. This is a useful skill in many different situations. For example, Caleb scored 15 points in the basketball game Saturday, and 20% more points in the game Tuesday. How many points did Caleb score Tuesday? This is a percent problem that we solve by multiplying. First, what is 20% of 15? 15 x 20/100. Remembering that 15 can be written as 15/1, we can write 15/1 x 20/100. Then we multiply the numerators (tops) and the