Class 8 Adding and Subtracting Expressions — practice questions with answers

Algebra · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.

1. How many terms are there in

4 x^{2} - 3 x y + 7

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Answer: D) 3

Terms are separated by + or − signs:

4 x^{2}

- 3 x y

and

7

. So there are 3 terms.

2. Simplify:

5 a + 3 b - 2 a + 4 b

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Answer: B)

3 a + 7 b

Combine like terms:

(5 a - 2 a) + (3 b + 4 b) = 3 a + 7 b

. Unlike terms a and b cannot be merged into ab.

3. A path goes from A to B to C to D. The figure gives each part of the path. What is the total length?

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Answer: D)

6 x + 3

(2 x + 1) + (x + 4) + (3 x - 2) = 6 x + 3

4. The sum of two expressions is

9 a - 4 b

. One of them is

5 a + 2 b

. Find the other.

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Answer: D)

4 a - 6 b

Other

= (9 a - 4 b) - (5 a + 2 b) = 4 a - 6 b

5. A rectangle is split into two parts as shown. Find the perimeter of the whole (outer) rectangle.

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Answer: B)

12 x + 14

Length

= (3 x + 2) + (x + 5) = 4 x + 7

; breadth

= 2 x

. Perimeter

= 2 (4 x + 7 + 2 x) = 12 x + 14

10 x + 14

counts the breadth only once.

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