Q: Alexa and Emily open up a lemonade stand in the front yard. They spent $10 for lemons, $5 for sugar and $3 for cups. The lemonade is $4 a cup. They sell a total of 21 cups. How much profit did Alexa and Emily make after paying off expenses?
A: Alexa and Emily spend a total of $10 + $5 + $3 = $18. They make a total of $4 x 21 = $84. They make a profit of $84 - $18 = $66. The answer is 66.

Q: Out of the 80 students who took the biology exam, only 2/5 of them managed to score 100%. If a score below 80% qualified as failing, and 50 percent of the remaining students who didn't score 100% managed to score over 80%, calculate the number of students who failed the exam.
A: The number of students who scored 100% is 2 / 5 * 80 = 32. Out of the 80 students, 80 - 32 = 48 did not score 100%. If 50% of the students who did not score 100% managed to score over 80%, then 50 / 100 * 48 = 24 students scored over 80%. The number of students who failed is 48 - 24 = 24. The answer is 24.

Q: Jeff was driving to the capital city to attend a conference. At first, he was driving at 80 miles/hour for about 6 hours, then the speed limit changed and he had to slow down to 60 miles/hour, and so he drove at this speed for 4 hours. Then he made a stop at a gas station. Once the car was full of gas, he drove at 40 miles/hour the rest of the trip for 2 hours. How many miles did he travel?
A:
In the first stretch he drove 80 miles / hour x 6 hours = 480 miles. In the second stretch he drove 60 miles / hour x 4 hours = 240 miles. After the gas station he drove 40 miles / hour x 2 hours = 80 miles. In total he drove 480 miles + 240 miles + 80 miles = 800 miles. The answer is 800.