JAMB Mathematics 2020 past questions

Checked by the Skolra question team · Last updated 23 October 2026

Ten questions from the 2020 JAMB Mathematics paper, with answers and explanations. We hold 40 questions from this paper, and the Skolra app has all of them.

JAMB Mathematics 2020 questions and answers

1. 1.Find the simple interest rate percent annum at which N1000 accumulates to N1240 in 3 years.
   1. A
      8% per annum
      Correct
   2. B
      6% per annum
   3. C
      24% per annum
   4. D
      12% per annum
   Show answerHide answer

   Answer: A

   Step 1: Find the interest earned. Interest = Amount − Principal = ₦1240 − ₦1000 = ₦240.

   Step 2: Use the simple interest formula I = PRT/100, where P = ₦1000, T = 3 years, and I = ₦240.

   240 = (1000 × R × 3)/100
   240 = 30R
   R = 240/30 = 8

   So the rate is 8% per annum — this is the correct answer.

   A candidate who forgets to divide by the 3 years lands on 24%, since 240/1000 × 100 = 24, ignoring the time period entirely. Someone who rounds or misplaces a digit while dividing might arrive at 12% or 6%, but neither satisfies 1000 × R × 3/100 = 240. Only 8% per annum, over 3 years, on ₦1000 principal, produces exactly ₦240 interest and brings the amount to ₦1240.

2. 2.

   Simplify $\frac{324 - 4x^2}{2x + 18}$

   1. A
      18 - 2x
      Correct
   2. B
      18 + 2x
   3. C
      9 - x
   4. D
      2x - 18
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   Answer: A

   324 − 4x² is a difference of two squares once you take out the common factor 4:

   324 − 4x² = 4(81 − x²) = 4(9 − x)(9 + x)

   The bottom, 2x + 18, factorises as 2(x + 9).

   So the fraction becomes:

   4(9 − x)(9 + x) / [2(x + 9)]

   Since (9 + x) and (x + 9) are the same thing, they cancel, leaving:

   4(9 − x) / 2 = 2(9 − x) = 18 − 2x

   That is the correct simplification.

   Where the wrong options come from:
   18 + 2x comes from mixing up the sign when expanding 2(9 − x).
   2x − 18 is the same result but with the overall sign flipped — a common slip when cancelling.
   9 − x looks tidy but forgets to bring down the factor of 2 that survives after cancelling 4/2.

3. 3.

   Evaluate (212)$_3$ - (121)$_3$ + (222)$_3$

   1. A
      (1021)₃
   2. B
      (1020)₃
      Correct
   3. C
      (1002)₃
   4. D
      (1012)₃
   Show answerHide answer

   Answer: B

   Step 1: Convert each base-3 number to base 10.
   (212)₃ = (2×3²) + (1×3¹) + (2×3⁰) = 18 + 3 + 2 = 23
   (121)₃ = (1×3²) + (2×3¹) + (1×3⁰) = 9 + 6 + 1 = 16
   (222)₃ = (2×3²) + (2×3¹) + (2×3⁰) = 18 + 6 + 2 = 26

   Step 2: Do the arithmetic in base 10.
   23 − 16 + 26 = 7 + 26 = 33

   Step 3: Convert 33 back to base 3.
   33 ÷ 3 = 11 remainder 0
   11 ÷ 3 = 3 remainder 2
   3 ÷ 3 = 1 remainder 0
   1 ÷ 3 = 0 remainder 1
   Reading the remainders from bottom to top gives (1020)₃, which checks out: (1×27)+(0×9)+(2×3)+(0×1) = 27 + 6 = 33.

   This is confirmed by working directly in base 3: (212)₃ − (121)₃ gives (021)₃ after borrowing correctly, and (021)₃ + (222)₃ gives (1020)₃ after carrying correctly.

4. 4.

   A school boy lying on the ground 30m away from the foot of a water tank towel observes that the angle of elevation of the top of the tank is 60$^o$. Calculate the height of the tank.

   1. A
      15 m
   2. B
      15√3 m
   3. C
      10√3 m
   4. D
      30√3 m
      Correct
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   Answer: D

   The boy, the foot of the tank, and the top of the tank form a right-angled triangle. The distance along the ground (30m) is the side adjacent to the angle of elevation, and the height of the tank is the side opposite it.

   Since tangent relates the opposite and adjacent sides:

   tan 60° = height ÷ 30

   height = 30 × tan 60° = 30 × √3 = 30√3 m

5. 5.

   A sector of circle of radius 7.2cm which substends an angle of 300$^o$ at the centre is used to form a cone. What s the radius of the base of the cone?

   1. A
      8.64cm
   2. B
      6.0cm
      Correct
   3. C
      3.6cm
   4. D
      1.2cm
   Show answerHide answer

   Answer: B

   Correct answer: 6.0cm

   When a sector is folded round to make a cone, the sector's radius becomes the cone's slant height, and the sector's arc length becomes the circumference of the cone's circular base.

   Arc length of the sector = (θ/360) × 2πR = (300/360) × 2π × 7.2cm = 12π cm.

   Setting this equal to the base circumference of the cone, 2πr:
   2πr = 12π
   r = 6cm

   A quicker route is the direct relation r = R × (θ/360°), which gives the same 6cm since the 2π on both sides cancels.

6. 6.

   Find the equation of the line through the points (5, 7) parallel to the line 7x + 5y = 12.

   1. A
      7x + 5y = 12
   2. B
      7x - 5y = 70
   3. C
      5x + 7y = 70
   4. D
      7x + 5y = 70
      Correct
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   Answer: D

   Step 1: Find the gradient of the given line.
   Rewrite 7x + 5y = 12 in the form y = mx + c: 5y = -7x + 12, so y = -7/5 x + 12/5. The gradient is -7/5.

   Step 2: A parallel line has the same gradient.
   So the required line also has gradient -7/5 and passes through (5, 7).

   Step 3: Use the point-gradient form.
   y - 7 = -7/5(x - 5)
   Multiply through by 5: 5y - 35 = -7x + 35
   Collect terms: 7x + 5y = 70

   Check: substituting (5,7): 7(5) + 5(7) = 35 + 35 = 70. This confirms 7x + 5y = 70 is correct.

7. 7.

   Inpreparing rice cutlets, a cook used 75g of rice, 40g of margarine, 105g of meat and 20g of bread crumbs. Find the angle of the sector which represent meat in a pie chart?

   1. A
      112.5°
   2. B
      120°
   3. C
      157.5°
      Correct
   4. D
      105°
   Show answerHide answer

   Answer: C

   Total mass of all ingredients = 75g (rice) + 40g (margarine) + 105g (meat) + 20g (bread crumbs) = 240g.

   In a pie chart, each item's angle is its fraction of the total, multiplied by 360°. For meat:

   Angle = (105/240) × 360° = 157.5°

   So the correct angle for the meat sector is 157.5°.

8. 8.

   Three consecutive terms of a geometric progression are given as n - 2, n and n + 3. Find the common ratio

   1. A
      3
   2. B
      3/2
      Correct
   3. C
      4/3
   4. D
      2/3
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   Answer: B

   In a geometric progression, the square of the middle term equals the product of the two terms on either side of it:

   n² = (n − 2)(n + 3)

   Expanding the right side: n² = n² + n − 6, which simplifies to n = 6.

   So the three terms become 4, 6 and 9. The common ratio is 6 ÷ 4 = 9 ÷ 6 = 3/2, and this checks out consistently across both pairs of terms.

   A candidate who inverts the ratio (dividing the smaller term by the larger) lands on 2/3 instead. Mixing up which pair of terms to divide, or making an arithmetic slip while expanding (n − 2)(n + 3), can also produce 4/3 or 3 as tempting but incorrect results.

9. 9.

   Reach each number to two significant figures and then evaluate $\frac{0.02174 \times 1.2047}{0.023789}$

   1. A
      1.1
      Correct
   2. B
      1.15
   3. C
      1.0
   4. D
      11.0
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   Answer: A

   First round each number to two significant figures:

   0.02174 → 0.022
   1.2047 → 1.2
   0.023789 → 0.024

   Now evaluate: (0.022 × 1.2) ÷ 0.024 = 0.0264 ÷ 0.024 = 1.1.

   This matches closely with the unrounded calculation, (0.02174 × 1.2047) ÷ 0.023789 ≈ 1.101, confirming that 1.1 is correct.

   The result of 1.15 comes from a common rounding mistake: chopping 0.023789 down to 0.023 (truncating) instead of correctly rounding it up to 0.024 at the third significant figure.

   The result of 1.0 comes from rounding each number too aggressively, to only one significant figure (0.02, 1, 0.02), which is not what the question asked for.

10. 10.

    In a class of 40 students, 32 offer mathematics, 24 offer physics and 4 offer neither mathematics nor physics. How many offer both mathematics and physics?

    1. A
       20
       Correct
    2. B
       16
    3. C
       12
    4. D
       24
    Show answerHide answer

    Answer: A

    Step 1: Find how many students offer at least one of the two subjects. Since 4 offer neither, that leaves 40 − 4 = 36 students who offer mathematics or physics (or both).

    Step 2: Add the two given totals: 32 (mathematics) + 24 (physics) = 56. This counts the students who offer both subjects twice.

    Step 3: Use the union rule: n(Maths ∪ Physics) = n(Maths) + n(Physics) − n(Both). So 36 = 56 − n(Both), which gives n(Both) = 56 − 36 = 20.

The questions come from past JAMB, WAEC and NECO papers. We use software to help write the answer options and explanations, and every answer is checked twice before it goes on the site. How we check

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