Strontium-90 is a radioisotope that will decrease in mass by one-half every 29 years. How many years will it take for a 10.0-gram sample of strontium-90 to decay to 5.00 grams?
Answer

1

14.5

29

58

Question

Strontium-90 is a radioisotope that will decrease in mass by one-half every 29 years. How many years will it take for a 10.0-gram sample of strontium-90 to decay to 5.00 grams?
Answer
		
1
		
14.5
		
29
		
58

anonymous · Answer

I think the answer is 29...only one half-life would have to pass right? Someone said two half lives would have to pass, that's why I'm confused. ??

anonymous · Answer

@ganeshie8  @iambatman

anonymous · Answer

wait no sorry i meant d.

anonymous · Answer

so it is two half lives?
how?

anonymous · Answer

d = 58 is right. this is because a half life means it decreases by 1/2 so it's 2 and a half divided by 10. and this is the equivalent of 1/4. and yes, it is two half lives because 1/4 = 2 half lives. so, you do c) 29 x 2, which is 58!

anonymous · Answer

um...wouldn't 10 be divided by .5?
1/2 is .5 in decimal form...

anonymous · Answer

no. 2.5 so its 10/2.5

anonymous · Answer

why?

anonymous · Answer

sorry i meant the ether way. so t's 2.5/10 because it has to match with the 2 half lives

anonymous · Answer

1/4 and 2 match together... i don't know how to explain

anonymous · Answer

I still don't quite understand, but thanks for your help anyway. :)

anonymous · Answer

well if you think it's 29, put 29. I'm positive the answer is 58 though.