Alex collects stamps. he wants to buy a superhero set for $3.88, a president set for $5.88, and a dinosaur set for $3.88. he has $15 to spend on stamps. which statement best describes whether an exact total or an approximate total should be calculated? a. alex must add the 3 amounts exactly so he will know if he has enough money to buy the stamps. b. alex can round the prices of the stamps to the nearest dollar and then add to estimate if he has enough money.