A ratio compares parts, and most Ratios, proportions; distance-rate-time questions turn on keeping those parts in step.
If two quantities are in the ratio two to three, they can be written as two times some number and three times the same number, which turns a wordy setup into a simple equation. Unit-price problems use the same idea: find the cost of one unit, then scale up.
Distance-rate-time items rest on distance equals rate times time, and a well-known misconception is averaging two speeds directly when the times spent at each speed differ. Answer choices frequently include the result of setting a proportion upside down.
Sample questions
Pick an answer to see whether it is right — nothing is saved, and nothing needs an account.
Question 1Mid
x and y are positive numbers, and yx=32.
Column A
Column B
x+6
y+4
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Answer: D — The relationship cannot be determined from the information given
Let x=2k and y=3k. Then the columns are 2k+6 and 3k+4. Different positive values of k make Column A greater, equal, or less, so the relationship cannot be determined.
Question 2Mid
Three positive numbers are in the ratio 2:3:5. If 12 is added to the smallest number and 6 is subtracted from the largest number, the two resulting numbers are equal. What is the middle number?
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Answer: B — 18
Let the three numbers be 2k,3k, and 5k. The changed smallest and largest numbers are equal, so 2k+12=5k−6. This gives 18=3k, so k=6. The middle number is 3k=18.
Question 3Easier
A florist pays 4.50 dollars for 3 meters of ribbon. Every meter has the same price. How much, in dollars, will 8 meters of ribbon cost?
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Answer: C — 12.00
The unit price is 4.50/3=1.50 dollars per meter. Therefore, 8 meters cost 8×1.50=12.00 dollars.
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