The half-life of a radioactive substance is 30 minutes. The time (in minute) taken between 40% decay and 85% decay of the same redioactive substance is
(a) 15 (b) 30
(c) 45 (d) 60
(d) Key idea Half-life of a radioactive substance is log
Putting these in the formula
So, two half-life periods has passed.
Thus, time taken=2 min