Grace starts with 100 milligrams of a radioactive substance. The amount of the substance decreases by 14
1
4
each week for a number of weeks, w. She writes the expression 100(14
1
4
)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.