A radioactive sample has a half-life of 10 min.What fraction of the sample is left after 40 min?
A) 1/2
B) 1/4
C) 1/8
D) 1/16
E) 1/32

Question

Quizplus · Accepted Answer

After the first half-life (10 min), the sample is reduced to 1/2 of its original size. After the second half-life (20 min), it is reduced to 1/2 of that size (1/2 x 1/2 = 1/4). After the third half-life (30 min), it is reduced to 1/2 of that size again (1/2 x 1/4 = 1/8). Finally, after the fourth half-life (40 min), it is reduced to 1/2 of that size one more time (1/2 x 1/8 = 1/16). Therefore, the fraction of the sample left after 40 min is 1/16.

A Radioactive Sample Has a Half-Life of 10 Min