21 w = 105 is the next step if you match the "cross products" of numerator-denominator pairs.
Then divide each side by 21 to get w.
I am working on cross products of proportions. one question is 5/7 = 3w/21
Can someone help?
2 answers
multiply both sides of this equation by 21
(5/7) 21 = (3w/21) 21
5*3 = 3 w
now divide both sides by 3
5 = w
(I do not like the cross multiplication language. It is safer to multiply both sides by a common multiple of the denominators, which is really what cross multiplication means.)
If you did it with cross multipication you would have
5 * 21 = 7 * 3 * w
5 * 21 = 21 * w
5 = w
(5/7) 21 = (3w/21) 21
5*3 = 3 w
now divide both sides by 3
5 = w
(I do not like the cross multiplication language. It is safer to multiply both sides by a common multiple of the denominators, which is really what cross multiplication means.)
If you did it with cross multipication you would have
5 * 21 = 7 * 3 * w
5 * 21 = 21 * w
5 = w
2 answers