Proportional Reasoning

Basic Algebra...we need this to cross multiply.

x + 3 = 5 is an equation with an unknown number...a variable (x)

we can use the math in the question to solve for x, so we can do 5-3 = 2

x - 4 = 7, we can use the math to do the opposite, so 7 + 4 = 11...

if the question was 5 times x = 20, it's asking 5 times what equals 20? so we can do the opposite math to get 20 divided by 5 = 4... the answer

BIG MESSAGE! We can do the opposite math to get the answer...

5 times x = 5x

if 5x=30 we can find x by doing the opposite...30/5 (30 divided by 5). = 6

Examples:

6x = 12

8x = 3.45

2x = 15

Why do we need to know this?

Sometimes our equivalent fractions are called "proportions" and the numbers don't work evenly...and we need a mathy way to get the answer!

so what we do is "cross multiply"multiply the bottom of one fraction with the top of the other and vice versa!

Practice these...