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45 votes
45 votes
The half-life for a 200 gram sample of radioactive element X is 5 days. How much of element X remains after 15 days have passed?

A. 200 g - no change

B. 25 g

C. 50 g

D. 12.5 g

User Rebeku
by
2.7k points

1 Answer

22 votes
22 votes

Answer:

B.) 25g

Step-by-step explanation:

The easiest way to solve this problem is to realize that the sample has gone through three half-lives (15÷5=3).

Use this information to calculate how much of the original 200g sample is left after the three half-lives:


((1)/(2))(200g)=100g\\((1)/(2))(100g)=50g\\((1)/(2))(50g)=25g

So, after three half-lives, the remaining sample has a mass of 25g.

User Praveen Prajapati
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3.2k points