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Chapter 3 · Question 4

Solve $x-2y=0$ and $3x+4y=20$ by substitution.

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Answer

Direct Answer

From

x-2y=0

,

x=2y

. Substitute in

3x+4y=20

:

3(2y)+4y=20

, so

10y=20

,

y=2

. Hence

x=4

.

Simple Explanation

Use the first equation to write

x=2y

, then substitute. The answer is

(4,2)

.

Exam-Ready Structure

Given

x-2y=0

, we get

x=2y

. Substitute this in

3x+4y=20

:

3(2y)+4y=20

, so

6y+4y=20

, hence

10y=20

and

y=2

. Then

x=2(2)=4

. Therefore the solution is

x=4,y=2

.

Key Points

From $x-2y=0$ , $x=2y$ .

Related Questions

Solve $2x+3y=11$ and $2x-y=3$ by elimination.

State the cross-multiplication formula for solving a pair of linear equations.

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