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anonymous
 4 years ago
Strontium90 has a halflife of 29 years. In how many years will a 1 kg sample of strontium90 decay and reduce to 0.25 kg of strontium90?
Answer
58 years
116 years
87 years
29 years
anonymous
 4 years ago
Strontium90 has a halflife of 29 years. In how many years will a 1 kg sample of strontium90 decay and reduce to 0.25 kg of strontium90? Answer 58 years 116 years 87 years 29 years

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anonymous
 4 years ago
Best ResponseYou've already chosen the best response.058 years. Use this expression: \[\ aA=Ae^{kt} \] Where: A  is the initial amount (1 kg) a  percentage of A left after time t ( 0<a<1 ) k  constant (that you can find from knowing the halflife) t  time passed So you know that after t=29 years there is 0.5A left. From that you can calculate k and use it to calculate how much time it takes to drop to 0.25 percent of initial amount. It is even easier to do this if you notice that 0.25 is half of half life. So it drops by a half in 29 years and by another half in another 29 years. In each 29 years the amount halves itself. so it goes: 0 years  1kg 29 years 1/2*1kg 2*29years  1/2*1/2 *1kg (this is what you are asked for) 3*29years 1/2*1/2*1/2*1kg 4*29years 1/2*1/2*1/2*1/2*1kg
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