SOLUTION: xgrammes of radioactive is isotope decayed to 5g in 100 days.the half life of the isolate is 25 days.calculate mass x

Question 772377: xgrammes of radioactive is isotope decayed to 5g in 100 days.the half life of the isolate is 25 days.calculate mass x
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
What's probably expected is blind application of a memorized formula involving while using a calculator and talking about exponential functions and exponential decay.

THE FANCY WAY:
Exponential decay functions state that the amount remaining after a time is related to the initial amount and the half-life } by the function
or the corresponding exponential
Substituting the values given,
-->-->-->
-->-->-->-->

THE CONCEPTUAL, MENTAL MATH WAY:
However, days is half lives, and that means the amount was halves 4 times, and is now of the original amount.
Doubling the final 5g amount 4 times, gives us the original amount as

The calculation can be done without touching pencil or calculator.
5 --> 10 --> 20 --> 40 --> 80
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