Problem 7 · 2004 AMC 8
Easy
Arithmetic & Operations
two-step-calculation
An athlete's target heart rate, in beats per minute, is 80% of the theoretical maximum heart rate. The maximum heart rate is found by subtracting the athlete's age, in years, from 220. To the nearest whole number, what is the target heart rate of an athlete who is 26 years old?
Show answer
Answer: B — 155 bpm.
Show hints
Hint 1 of 2
Read the recipe in order, and resist the tempting shortcut. The 80% applies to the maximum — which you must build first — not to 220. Doing the steps out of order is the trap the problem is testing.
Still stuck? Show hint 2 →
Hint 2 of 2
The skill is respecting operation order in word problems: build each quantity the sentence describes before combining. 'Percent of (something you compute)' — compute the something first.
Show solution
Approach: build the max, then take 80%
- Step 1 — the maximum: 220 − 26 = 194. This must come first; 80% of 194 is a very different number from 80% of 220.
- Step 2 — the target: 0.80 × 194 = 155.2, which rounds to 155.
- Why eliminate 176? That's 80% of 220 — the classic 'skipped the subtraction' answer the test bakes in to catch the rush.
Mark:
· log in to save