A shoe salesman earns a commision of 20% of all shoe sales made. Yesterday he sold 2 pairs of shoes for 80$ each and 3 pairs of shoes for $70 each. How much did he earn in commission yesterday?

You can calculate 20% of a number (or any percentage of a number by moving the decimal one place to the left in both number) so 20% of 80 = 2x8 = 16. He made $16 on one pair of $80 shoes. So for selling two pairs of $80 shoes, he made $32. He then sold 3 pairs of $70. 2x7 = 14. 14x3 = 42. He made $42 on the three pairs of $70 shoes so 42 + 32 = 74. He made 74 dollars in commission