Answer:
a) greater than 20
b) 20 is the estimate (round all the three other numbers and add, then subtract from 80 because 20, the average, times the four meetings is 80)
c) You can check your estimate by adding all of the numbers and subtracting the answer by 80. 18 + 17 + 21 = 56. 80 - 56 = 24
24 is closer to 20 than 30, so our estimate is correct.
Explanation: