Why do fractions need to have a common denominator before you add or subtract them?

Which of the following is a function? a.) {(-2, -4/5), (-1,-,,-1)} b.) {(-2,,1/,3/,1)} c.) {(-22)} d.) {(-21)}

For the chance to be team captain, the numbers 1-30 are put in a hat and you get two chances to pick a number, without replacement. which formula correctly shows how to find the probability that you choose the number 1 and then 2?

Apackage of orgainc strwberries costs $1.50 while there in season and $2.25 when not in season what the percent increase