ACT Math Practice Question #1268 (Medium (31)) | Test Citadel
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ACT Math Difficulty: Medium (31)

Digital ACT Math Practice Question #1268

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A sample of Bismuth-212, commonly utilized as a alpha-radiation targeted therapy, exhibits an initial radioactivity of $1280\text{ megabecquerels (MBq)}$. The half-life of Bismuth-212 is $60\text{ minutes}$. What is the remaining radioactivity of the sample, in MBq, after exactly $300\text{ minutes}$ have elapsed?
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Socratic AI Engine Step-by-Step Derivation
0ms Precomputed
⚡ 15-Second Desmos Speed Hack

Divide by 2 repeatedly: $1280 \rightarrow 640 \rightarrow 320 \rightarrow 160 \rightarrow 80 \rightarrow 40$. Takes under 10 seconds.

Masterclass Solution & Distractor Trap Analysis

Calculate the number of half-lives elapsed: $n = \frac{\text{Total Time}}{\text{Half-life}} = \frac{300}{60} = 5$. The remaining activity is given by $A = A_0 \left(\frac{1}{2}\right)^n = 1280 \left(\frac{1}{2}\right)^{5} = \frac{1280}{32} ...

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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