One hundred days after the leak, 11% of the original amount of the substance remained. Determine the half-life of this radioactive isotope.

Question

The half life is about how many days?

Answer 1

If 11% is left to find out what decayed we subtract 11% from 1

1-.11=.89

Then do a proportion

.89/100 = .50/x

Cross multiply

.89x=(.50)(100)

Divide both sides by .89

X is approximately 56 days