Question

a teacher had 21 red pens. if the ratio of red pens to blue pens owned was 3:1 how many pens did she have in total

Answer 1

If the ratio of red to blue pens is 3:1, we can find the amount of blue pens by multiplying by 1/3, to get 21*1/3=7.  There are 21 red pens and 7 blue pens, so there are 21+7=28 pens total.