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Lesson · Grade 7 · Mathematics

Two-Step Equations: Undo Each Step

  • Grade 7
  • Mathematics
  • 1 min 7 s
  • British Columbia
  • BC7-MA-43

To solve 4x + 5 = 33, the video first shows what happens to x: it is multiplied by 4, then 5 is added. It then undoes those steps in reverse order on both sides, subtracting 5 and then dividing by 4, to find x = 7, and checks that 4 × 7 + 5 = 33.

Concept: Two-step equations by undoing each step

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In one sentence

The question this lesson answers

Let us solve the equation 4x plus 5 equals 33.

Think about the steps that turn x into 33.

Transcript

What the lesson says

Let us solve the equation 4x plus 5 equals 33.

Think about the steps that turn x into 33.

First, x is multiplied by 4, which gives 4x.

Then 5 is added, which gives 33.

To find x, work backwards from 33 and undo each step.

The last step was adding 5, so subtract 5 from both sides.

33 minus 5 is 28, so 4x equals 28.

Before that, x was multiplied by 4, so divide both sides by 4.

28 divided by 4 is 7, so x equals 7.

Check it: 4 times 7 is 28, and 28 plus 5 is 33.

It works, so x equals 7 is right.

To solve a two-step equation, undo each step on both sides, starting with the last one.

Curriculum

Where this fits

British Columbia, Grade 7

Mathematics, Patterns and algebra: two-step equations with whole-number coefficients, constants, and solutionsBC7-MA-43

Previous: Two-step equations on a balanceNext: Checking a Solution by Substituting

The outcomes and strands follow the British Columbia curriculum.

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