If element X has a half life of 25 years, what fraction of a sample of element X would remain after 50 years?

a.) 3/4
b.) 1/8
c.) 7/8
d.) 1/2
e.) 1/4

Question

If element X has a half life of 25 years, what fraction of a sample of element X would remain after 50 years?
 		
a.) 3/4
b.) 1/8
c.) 7/8
d.) 1/2
e.) 1/4

jfraser · Answer

how many half-lives will pass after 50 years if each half-life is 25 years?

anonymous · Answer

I don't know, 5?

jfraser · Answer

what's 50 divided by 25?

anonymous · Answer

2

jfraser · Answer

so 25 years + 25 years = 50 years = 2 half-lives, ok so far?

anonymous · Answer

yes.

jfraser · Answer

so, after each half life, HALF of the sample will decay, no matter how much you started with,  the amount will always be cut in half for the next half-life

jfraser · Answer

so if you start with 100% of a sample, after one half life, you'll have 50% remaining.

jfraser · Answer

after a SECOND half-life, half of the 50% will remain, and what's half of 50%?

anonymous · Answer

25

jfraser · Answer

so what's the fraction that means the same thing as 25%?

anonymous · Answer

e?