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A certain radioactive substance has a half-life of 40 minutes. How much of an original 100 grams substance will remain after 2 hours?

solution) m= m0/2t/T

m=100 gms..

t=2 hours=2*60=120 min..

T=40 min

m=100/2120/40

m=100/23

m=100/8

m=12.5 gms.

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