Problem 3 · 2010 AMC 8
Easy
Fractions, Decimals & Percents
percent-increase
The graph shows the price of five gallons of gasoline during the first ten months of the year. By what percent is the highest price more than the lowest price?
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Answer: C — 70%.
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Hint 1 of 2
‘More than’ is the key phrase: you're comparing the gap to the starting amount, not to the bigger amount. The low price is the baseline (the 100%).
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Hint 2 of 2
Percent change always divides by where you started: (new − old) / old. The word after ‘than’ tells you the baseline.
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Approach: compare the gap to the baseline (the low)
- Read the tallest and shortest bars: highest = 17, lowest = 10. The gap is 17 − 10 = 7.
- ‘How much more than the low’ means measure that gap against the low: 7 / 10 = 0.7 = 70%.
- Watch out: a common trap is dividing by 17 (the high). Dividing by the wrong number is exactly why the wrong answers are on the list — always anchor to the amount named after ‘than.’
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