The best estimate is b. \$$310$.
Work Step by Step
We know that the most expensive calculator is approximately \$$40$, and the least expensive one is approximately \$$20$, and half ($5$) calculators cost approximately \$$30$. The total cost of those calculators is: $20+5*30+40=210$ The average cost of those $7$ calculators is $270\div7=30$ If that was also the average cost of the $10$ calculators, then the total price would be: $10*30=300$ In the cheapest possible case, the remaining 3 calculators would all cost \$$20$, which would make the total price: $210+3*20=270$ In the most expensive case, the remaining calculators would all cost \$$40$, which would make the total price: $210+3*40=330$ The four possible answers for the best estimate of the price are: a. \$$240$ b. \$$310$ c. \$$345$ d. \$$355$ Out of these four, looking at all the possible sums, the best estimate is b. \$$310$.