C. 75 dollars (is the best estimate for the cost of the 10 calculators)
Work Step by Step
We are told that half of the 10 people ordered calculators costing 6.95 each. Therefore, this means 5 people paid approximately 7 dollars per calculator. 5 x 7 = 35 dollars. Then, there are still 5 more people buying calculators. Since we don't know what price each paid, we can average the lowest priced calculator and the highest price calculator. Estimating, the lowest cost is about 5 dollar and the highest price is about 13 dollars. The average of 5 and 13 is 9 dollars. So, if the other 5 people paid an average of 9 dollars per calculator, then 5 x 9 = 45 dollars. Add the 35 and 45 and we get 80 dollars. The answer choice closest to this is answer C, 75 dollars.