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.