Grace starts with 100 milligrams of a radioactive substance. The amount of the substance decreases by 14 each week for a number of weeks, w. She writes the expression 100(14)w to find the amount of radioactive substance remaining after w weeks. Ryan starts with 1 milligram of a radioactive substance. The amount of the substance decreases by 40% each week for a number of weeks, w. He writes the expression (1 – 0.4)w to find the amount of radioactive substance remaining after w weeks.

Use the drop-down menus to explain what each part of Grace’s and Ryan’s expressions mean.

Grace’s Expression: 100(14)w

100:

14:

w:

(14)w:

Ryan’s Expression: (1 – 0.4)w

1 – 0.4:

w:

0.4: