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ACT Math Videos 164 videos

ACT Math 1.1 Pre-Algebra
1061 Views

Pre-Algebra Drill 1, Problem 1. Calculate 23 + 53(7 – 4).

ACT Math 1.1 Trigonometry
355 Views

ACT Math: Trigonometry Drill 1, Problem 1. What is the length of y?

ACT Math 1.2 Coordinate Geometry
252 Views

ACT Math: Coordinate Geometry Drill 1, Problem 2. Solve the inequality and determine which solution is shown on the number line.

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ACT Math 1.3 Elementary Algebra 301 Views


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Description:

ACT Math Elementary Algebra: Drill 1, Problem 3. Solve for y using substitution.

Language:
English Language

Transcript

00:03

And here's your shmoop de jour...

00:05

Solve for y using substitution: 2x + 4y = 16

00:11

x + 3y = 12

00:13

And here are the potential answers...

00:18

OK, so what is this question asking?

00:21

Questions like this one are algebra's version of... puzzles. Except you don't have to

00:25

worry about getting that cardboard dust all over yourself.

00:28

The key is to isolate one of the variables cleanly...

00:31

...i.e. figure out just what y equals and then shove that result into the other equation

00:35

so we can get a real answer.

00:38

It doesn't matter which equation we solve, but let's start with the second because...

00:42

it's there. And we already have a variable all by its lonesome.

00:45

We can rewrite it as x equals 12 minus 3y.

00:48

So now, everywhere we see an "x" we can just substitute "12 minus 3y."

00:54

If we do so in the first equation, we get 2 times the quantity 12 minus 3y... plus the

01:01

4y and equals 16.

01:04

Distribute the 2 and we have 24 minus 6y plus 4y equals 16.

01:10

Simplify to get 8 minus 2y equals zero...

01:13

...and then 8 = 2y.

01:16

Then if we divide both sides by 2 and we get y equals... 4.

01:21

Answer C.

01:22

As in, "Cardboard dust."

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