80% of 20 is 80/100 x 20 = 16
So, kelly has used 16 stamps, and has 4 left
Since each term contains x, x= 0 is one answer Also as x^2 is a factor it has duplicity 2.
Factoring:-
x^2 (x^2 - 4x + 3) = 0
x^2( x - 3)(x - 1) = 0
so x = 3 and x = 1 are also zeros
Answer:- x = 0 (duplicity 2), x = 1 and x = 3.
20/5 = 4 half lives
so
<span>300 * (1/2)^4
</span>= 300 * 0.0625
=18.75 grams
