Adoctor prescribes a 500-mg antibiotic tablet to be taken every eight hours. just before each tablet is taken, 20% of the drug remains in the body. (a) how much of the drug is in the body just after the second tablet is taken? after the third tablet?

A doctor prescribes a 500-mg antibiotic tablet to be taken every eight hours. just before each tablet is taken, 20% of the drug remains in the body.

(a)    how much of the drug is in the body just after the second tablet is taken?

600 mg

after the third tablet?

720 mg

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)