ariana starts with 100 milligram of a radioactive substance the amount of the substance decreases by 20% each week each number for weeks w. the expression 100 (-0.2) finds the amount radioactive substance remaining w weeks.

It is the difference between the initial amount and the percent decrease.

Step-by-step explanation:

i think ...

The required expression is 100 - 0.2w

Step-by-step explanation:

Given,

Amount of radioactive substance = 100 mg

The substance decreases by 20% each week.

To find the remaining amount of the in w weeks.

Now,

Each week 20% = 0.2 of the substance will be decreased.

So, in w weeks 0.2*w of the the substance will be decreased.

Hence,

The remaining substance = 100 - 0.2w