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Solve Linear Equations with Rational Number Coefficients

Students solve multi-step linear equations whose coefficients and constants are fractions or decimals, using the distributive property and combining like terms. They apply inverse operations methodically to isolate the variable and check their answer by substitution.

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Solve Linear Equations with Rational Number Coefficients

Grade 8 · Linear Equations in One Variable · question 1 of 3

0 of 20

20 rungs. A star at the top.

(1/2)x + 3 = 5, x =

How it is taught

0:00 of 3:32

Undo the add or subtract first.

Then multiply by the reciprocal of the coefficient.

Read it: Equations with a fraction of x

(1/4)x + 6 = 14: take 6 away, so (1/4)x = 8. That is 1 of 4 equal parts of x, so x = 4 × 8 = 32.

  1. Undo the adding first: take the number away from both sides.
  2. A fraction of x is 1 of its equal parts.
  3. Multiply that part by the number of parts to find x.

Undo in reverse: the + 6 came last, so it goes first.

(1/4)x is x cut into 4 equal parts, and 1 of them.

If 1 of 4 equal parts is 8, the whole is 4 parts of 8.

Take away, then multiply: (1/4)x = 8 means x = 4 × 8.

Dividing instead: 8 ÷ 4 = 2.

(1/4)x = 8 means x is 4 parts of 8: x = 32.

(1/2)x + 19 = 29, x = ___ — 20. Take 19 away from both sides: (1/2)x = 10. That is 1 of 2 equal parts of x, so x = 2 × 10 = 20.

½x + 1 = ¼x + 4

Let's solve a linear equation that has fractions in it. There's a clever first move that makes the rest easy.

Here's our equation: one-half x plus one equals one-fourth x plus four.

Look at the denominators — two and four. Their least common multiple is four. That's our magic number.

Solve: 12x + 1 = 14x + 4Step 1: clear the fractions.12x + 1=14x + 4LCD of 2 and 4 → 44 ·4 ·Multiply both sides by 42x + 4 = x + 16− x− xx + 4 = 16− 4− 4x = 1212(12) + 1 = 714(12) + 4 = 7✓ANSWERx = 12fractions cleared!
Grade 8 · Clear the fractions, then isolate x

Multiply every term on both sides by four. That cancels the denominators and clears the fractions.

Now we have whole numbers: two x plus four equals x plus sixteen.

Subtract x from both sides to gather the x terms on the left.

That leaves x plus four equals sixteen.

Now subtract four from both sides to isolate x.

And we get x equals twelve.

Let's check by substituting. One-half of twelve plus one is seven. One-fourth of twelve plus four is also seven. Both sides match.

x equals twelve. Nice work clearing those fractions!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics
Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal
1 star — one skill mastered, every rung of its ladder climbed
Climbing now
Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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