Thuy planned for a square table to have a side length of 30 in. but found that it could be a little bigger at 39 in. She found the change of scale below.

StartFraction 39 inches divided by 3 over 30 inches divided by 3 EndFraction = StartFraction 13 over 10 EndFraction. The change of scale is 13 to 10.

What is Thuy’s error

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.