Question

Question #24d75

Answer 1

7.5 grams.

Explanation:

Divide 12 hours by the half life of 3 hours to find the number of half lives.

`12/3 = 4` = the number of half lives.

A half life divides the amount by half so to find the mass left divide by `2 ^4` or `2 xx 2 xx 2 xx 2 =16`

so divide 120 grams by 16 or `2^4`

`120/16 = 7.5` grams.