Proportions
Do not fear.
Just 2 equal fractions my dear.
Scale, cross, or clear.
Then let out a big cheer!
Scale if mental math.
Cross or clear for direct path. SEE MORE EXAMPLES BELOW:)
AD is BC on cross, A = B AD =BC
C D
Learn it and be a math boss
Clearing fractions works just as well.
Know all three, you'll excel!
Cross Product Method OR Clear the Denominator Method
15 = 7 15 = 7
x 20 x 20
7x = (15)(20) (x ) (20)15 = 7 (x ) (20)
x 20
7x = 300 300 = 7x
7x = 300 300 = 7x 7 7 7 7
x = 300/7 300/7 = x
x = 40 + 20/7 40 + 20/7 = x
x = 42 4/7 42 4/7 = x