Percent Increase/Decrease

1. 120 comic books $$\eqalign{\dfrac{x}{150}&=\dfrac{20}{100}\\100x&=3000\\x&=30\\\\150-30&=120}$$

2. \$5.99 $$\eqalign{\dfrac{x}{39.95}&=\dfrac{15}{100}\\100x&=599.25\\x&=5.99}$$

3. \$33.96 $$\eqalign{\dfrac{x}{39.95}&=\dfrac{15}{100}\\100x&=599.25\\x&=5.99\\\\39.95-5.99&=33.96}$$

4. 66 questions $$\eqalign{\dfrac{x}{75}&=\dfrac{12}{100}\\100x&=900\\x&=9\\\\75-9&=66}$$

5. 9 questions $$\eqalign{\dfrac{x}{75}&=\dfrac{12}{100}\\100x&=900\\x&=9}$$

6. 54 problems $$\eqalign{\dfrac{x}{40}&=\dfrac{35}{100}\\100x&=1400\\x&=14\\\\40+14&=54}$$