A 10 pound block of lead-210 has a half-life of 22 years. What percentage of the block still contains lead-210 after 60 years?

1.5%

15%

77%

27%

The percentage of the block contains 15% after 60 years.

Explanation:

Step 1: Formula for half-life time

To calculate the half-life time we will use the following formula:

At = A0 * 1/2 ^ (x/t)

With At = the quantity after a time t

A0 = The quantity at time t = 0 (start)

x = time in this case = 60 years

t = half-life time = 22 years

Step 2: Calculate the percentage after 60 years

In this case: after 60 years the percentage will be

A0 = 10 * 1/2 ^ (60/22)

A0 = 1.5

A0 / At = 1.5 / 10 = 0.15

0.15 * 100% = 15 %

The percentage of the block contains 15% after 60 years.