KA-0151Ratio as parts of a whole
3 points, difficulty 1 of 3Level 7–8about 75sA bread recipe uses flour and sugar in the ratio 5 to 3. The two together weigh 320 grams. How much of that is flour?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
The ratio counts parts, not grams.
2The strategy
Five parts flour and three parts sugar make eight parts altogether. Find what one part weighs first.
3The full solution
320 divided by 8 is 40 grams per part. Flour is five parts, so 5 times 40 = 200 grams.
Solution
The reliable way
A ratio of 5 to 3 means the mixture is made of 5 + 3 = 8 equal parts. Divide the total by the number of parts: 320 / 8 = 40 grams per part. Flour is 5 parts, so it weighs 5 x 40 = 200 grams (and sugar is 3 x 40 = 120 grams, which checks out because 200 + 120 = 320). The transferable move: turn a ratio into a part size before you touch either quantity. The transferable idea: turn a ratio into a part size before you touch either quantity.
The elegant way
Flour is 5 of the 8 parts, so it is five eighths of 320, and five eighths of 320 is 200.
Why this is on the test: Almost every ratio mistake is answering for the wrong part or forgetting the parts must add to the whole.