1fourth times 1 eighth simplest form

Which term best describes the association between variables a and b? no association a negative linear association a positive linear association a nonlinear association a scatterplot with an x axis labeled, variable a from zero to ten in increments of two and the y axis labeled, variable b from zero to one hundred forty in increments of twenty with fifteen points in a positive trend.

1) prove that 731^3−631^3 is divisible by 100 2) prove that 99^3−74^3 is divisible by 25

Need plz been trying to do it for a long time and still haven’t succeeded