John is twice as old as mary. the sum of their ages is 21. how old is mary?
let j = john's age and m = mary's age.

In two or more complete sentences describe how to determine the appropriate model for the set of data, (1,1), (3,2), (6,3), (11,4).

Is the product of two rational numbers irrational or rational? first, make a hypothesis by multiplying two rational numbers. then, use variables such as x=a/b and y=c/d and the closure property of integers to prove your hypothesis.

The half-life of a certain material is 0.004 second. approximately how much of a 20-gram sample will be left after 0.016 second? a. 5 grams b. 16 grams c. 0.32 gram d. 1.25 grams