Jim is 5 years older than cindy. 4 years ago, the sum of their ages was 21. find each of their ages now.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

X+y=-4 x-y=2 use elimination with adding and subtraction

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.