Alyssa's ratio of correct questions to total questions is 16 : 20. 16 divided by 20 = 0.80 x 100% = 80%, Alyssa got a B on her quiz.
In order to get an A on the exam, Alyssa needs a ratio of 90 : 100. Looking at the solutions in part (a), 100 is 5 times 20 so to see how many questions Alyssa needs to answer correctly out of 20 we can divide 90 by 5. Since 90 ÷ 5 = 18, Alyssa needs to answer 18 questions correctly. The ratios 18 : 20 and and 90 : 100 are equivalent since both numbers are scaled by the same factor, 5, to get from the first pair of numbers to the second.
Jessie answered 3 times as many questions correctly than she did incorrectly. This means that for every 1 question Jessie answered incorrectly, she answered 3 questions correctly. In other words, Jessie's ratio of correct answers to incorrect answers is 3 : 1.
