Decimals

13 Grade 8 Mathematics questions on Decimals, with worked marking schemes. 13 questions are available on this topic in full.

1. Question 1

   3 marks

   Evaluate: 5.6 x 2.5 - 3.2 / 0.4

   (3 marks)

   Marking scheme

   Multiplication and division are done before subtraction, so work out those two parts first. (1)

   $5.6\times 2.5=14$, and $3.2÷0.4=8$ (because $0.4\times 8=3.2$). (1)

   Now subtract: $14-8=6$. (1)

   Final answer: $6$.

2. Question 2

   1 mark

   Write 0.0008 in standard form.

   A. $8\times 10^4$

   B. $8\times 10^{-3}$

   C. $8\times 10^{-4}$

   D. $0.8\times 10^{-3}$

   (1 mark)

   Marking scheme

   C. $8\times 10^{-4}$ — standard form needs a number between $1$ and $10$ times a power of ten. The point moves $4$ places to give $8$, and because the number is smaller than $1$ the index is negative. B moves only $3$ places and D leaves a number below $1$ in front.

3. Question 3

   1 mark

   Work out: 7.2 / 0.9

   A. 0.8

   B. 80

   C. 8

   D. 6.3

   (1 mark)

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4. Question 4

   1 mark

   Work out: 12.5 x 0.4

   A. 50

   B. 5

   C. 0.5

   D. 4.8

   (1 mark)

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5. Question 5

   1 mark

   Round 3.04967 to three significant figures.

   A. 3.04

   B. 3.06

   C. 3.049

   D. 3.05

   (1 mark)

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6. Question 6

   3 marks

   Sugar costs Ksh 125.50 per kilogram. Find the cost of 3.5 kg.

   (3 marks)

   Marking scheme

   The cost is the price for one kilogram multiplied by the number of kilograms: $125.50\times 3.5$. (1)

   Split the $3.5$ into $3+0.5$: $125.50\times 3=376.50$ and $125.50\times 0.5=62.75$. (1)

   Add the two parts: $376.50+62.75=439.25$. (1)

   Final answer: Ksh $439.25$.

7. Question 7

   1 mark

   Work out: 25.6 - 7.85

   A. 17.75

   B. 18.75

   C. 17.85

   D. 18.25

   (1 mark)

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8. Question 8

   3 marks

   A car uses 0.08 litres of fuel per kilometre. How far can it travel on 36 litres of fuel?

   (3 marks)

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9. Question 9

   1 mark

   Round 47.2685 to two decimal places.

   A. 47.27

   B. 47.06

   C. 47.3

   D. 47.269

   (1 mark)

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10. Question 10

    1 mark

    Work out: 3.45 + 12.8 + 0.07

    A. 15.32

    B. 16.22

    C. 16.32

    D. 4.62

    (1 mark)

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11. Question 11

    1 mark

    Work out: 4.8 / 0.6

    A. 0.8

    B. 8

    C. 80

    D. 0.08

    (1 mark)

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12. Question 12

    1 mark

    Write $\frac{3}{8}$ as a decimal.

    A. 0.375

    B. 0.38

    C. 0.835

    D. 2.667

    (1 mark)

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13. Question 13

    1 mark

    Work out: 0.6 x 0.05

    A. 0.3

    B. 0.11

    C. 0.011

    D. 0.03

    (1 mark)

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