Question

1. It is the time needed for half of a substance to decay.??​

Answer 1

The half-life (t1/2) is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value.

P/S 1: Are you sure that your question is related to maths?

+ Bonus: The half-life can be calculated from the decay constant as follows: half-life = ln (2) / (decay constant).

P/S 2: Not sure which is right tho:( Really sorry about that.