Nick starts with 20
20
milligrams of a radioactive substance. The amount of the substance decreases by 12
1
2
each week for a number of weeks,
w
. He writes the expression 20(12)
20
(
1
2
)
w
to find the amount of radioactive substance remaining after
w
weeks.

Autumn starts with 1
1
milligram of a radioactive substance. The amount of the substance decreases by 50%
50
%
each week for a number of weeks,
w
. She writes the expression (1−0.5)
(
1
-
0
.
5
)
w
to find the amount of radioactive substance remaining after
w
weeks.

Use the drop-down menus to explain what each part of Nick's and Autumn's expressions mean.