PLease help me with the answer please

Question

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass.Starting with 210 grams of a radioactive isotope, how much will be left after 4 half-lives?

Use the calculator provided and round your answer to the nearest gram.

______grams

Answer 1

The half life is the amount of time that it takes for the mass to be reduced by half. Your starting mass is 210 grams, and we want to know what the mass will be after four half lives. To determine this we need to divide the starting weight by 2 four times.

1st half life: 210/2= 105

2nd half life: 105/2=52.5

3rd half life: 52.5/2= 26.25

4th half life: 26.25/2= 13.125

Rounding to the nearest gram you would get 13 g.

Answer 2

After one half life: 210/2 = 105

After two half lives: 105/2 = 52.5

After three half lives: 52.5/2 = 26.25

After four half lives: 26.25/2 = 13.125 g = 13 grams

The "exponential equation" way to do this:

Amount = (Starting Amount)(1/2)^{number of half lives}

Amount = 210*(1/2)⁴

Amount = 13.125 grams = 13 grams