# Mathematics 2021 Past Questions | WAEC

Study the following Mathematics past questions and answers for JAMB, WAEC NECO and Post-JAMB. Get prepared with official past questions and answers for upcoming examinations.

- Correct, 0.00798516 to
**three**significant figures

- A. 0109
- B. 0800
- C. 00799
- D. 0.008

**Correct Option: Answer is C**

First 2 non-zero digits from the start, ignore the zeros and count from digit 7

0.00798516

0.00798516 =0.00799 to 3 s.f,

**2. **Simplify (11_{two})^{2}

- A. 1001
_{two} - B. 1101
_{two} - C. 101
_{two} - D. 10001
_{two}

**Correct Option: Answer is A**

11

__11__

11

__ 11__

__1001 _{two}__

**OR**

CONVERT TO BASE 10

(11_{two})^{2} = (11_{2}) × (11_{2})

= (1×2^{1})+(1×2^{0}) × (1×2^{1})+(1×2^{0})

= (1×2+1×1)×(1×2+1×1)

= (2+1)×(2+1)

= 3 × 3

= 9_{10}

Convert to binary number

2 | 9 |

2 | 4 r1 |

2 | 2 r0 |

2 | 1 r0 |

| 0 r1 |

=1001_{2}

**3. **Solve = 2\(^\sqrt{2x+1}\) = 32

- A. 13
- B. 24
- C. 12
- D.11

**Correct Option: Answer is C**

2\(^\sqrt{2x+1}\) = 32 ;

2\(^\sqrt{2x+1}\) = 2\(^5\)

\(\sqrt{2x+1}\) = 5

2x+1 =5^{2}

2x+1=25; 2x =25-1

2x =24; x =12

**4. **If log_{10}^{2} =m and log_{10}^{3} =n, find log_{10}^{24 }In term of m and n.

- A. 3m+n
- B. m+3n
- C. 4mn
- D. 3mn

**Correct Option: Answer is A**

log_{10}^{24 }= log_{10}^{4 x 3x 2}= log_{10}^{4}+ log_{10}^{3}+ log_{10}^{2}

2log_{10}^{2 }+ log_{10}^{3}+ log_{10}^{2}

=2m + n + m

3m+n

**5. **Find the 5^{th} term of the sequence 5, 10, 17, …….

**A.**22**B.**24**C.**36**D.**26

**Correct Option: Answer is D**

Add odd number beginning from 3 to the next number

2

2 + 3 = 5

5 + 5 = 10

10 + 7 = 17

17 + 9 = 26

The fifth term = 26

**6. **If P = {-3<x<1} and Q ={-1<x<3}, where x is a real number find, P n Q.

**A.**{-1<x<1}**B.**{-3<x<1}**C.**{-1<x<1}**D.**{-1<x<1}

**Correct Option: Answer is D**

**7. **Factorize 6pq-3rs-3ps + 6qr

**A.**(3r-p) (2q + s)**B.**3(p + r)(2q-s)**C.**3(p – r)(2q-s)**D.**(3r-p)(s-2q)

**Correct Option: Answer is B**

6pq – 3rs – 3ps +6qr

=3(2pq – rs – 3ps +2qr)

=(2pq – rs – 3ps +2qr)=(2pq-ps)+(2qr-rs)

=(2pq-ps)+(2qr-rs)

Factor out p in the first and r in the second

p(2q-s)+r(2q-s); (2q-s)(p+r)= 3(p + r)(2q-s)

**8. **What number should be subtracted from the sum of 2 1/6 and 2 7/12 to give 3 ¼.

**A.**1/3**B.**1 1/2**C.**1 1/6**D.**1/2

**Correct Option: Answer is B**

Let x be the number to be subtracted

2 1/6 +2 7/12 – x =3 1/4

=(13/6 + 31/12) – x = 13/4

=( 26 + 31 /12) -x =13/4; ( 57/12) – x =13/4

= 57/12 – x = 13/4; 57 -12x /12 = 13/4

= 4(57 – 12x)= 156; 228 – 48x = 156

-48x= 156 – 228;

X = 72/48; x = 3/2 = 1 1/2

**9. **Mensah is 5 years old and Joyce is **thrice **as old as Mensah. In how many years will Joyce be **twice **as old as Mensah?

**A.**3 years**B.**10 years**C.**5 years**D.**15 years

**Correct Option: Answer is C**

Let J = Joyce’s age

and M = Mensah’s age

(1) J = 3*M = 3*5 = 15 (for current ages)

(2) 2(5 + x) = 15 + x (for future ages, unknown is “x” years for condition 2xM = J to be met)

Multiply left side both by 2:

10 + 2x = 15 + x

Subtract x from both sides:

10 + x = 15

Subtract 10 from both sides:

x = 5

**10. **If 16 x 2^{(x+1)} = 4^{x} x 8^{(1-x)}, find the value of x.

**A. -4****B. 4****C.**1**D.**-1

**Correct Option: Answer is D**

= 16 x 2^{(x+1)} = 4^{x} x 8^{(1-x)}

= 2^{4} x 2^{(x+1)} =2^{2x }x 2^{3(x+1)}

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

collect like terms

-> x – 2x + 3x = 3 – 1 – 4

-> 2x = -2

-> x = -1

**11. **The circumference of a circular track is 9 km. A cyclist rides round it a number of times and stops after covering a distance of 302km. How far is the cyclist from the starting point?

**A.**5km**B.**6km**C.**7km**D.**3km

**Correct Option: Answer is A**

**12. **Simplify 2\(\sqrt{7}\) – \(\frac{14}{\sqrt{7}}\) + \(\frac{7}{\sqrt{21}}\)

**A.**\(\frac{\sqrt{21}}{21}\)**B.**7\(\frac{\sqrt{21}}{3}\)**C.**\(\frac{\sqrt{21}}{3}\)**D.**2\(\sqrt{3}\)

**Correct Option: Answer is B**

2√7- 14/√7 +7/√21

LCM is √21

**13. **If 4x +2y =16 and 6x – 2y = 4, find the value of (y-x)

**A.**8**B.**2**C.**4**D.**6

**Correct Option: Answer is B**

4x +2y =16 x 6

6x – 2y = 4 x 4

24x + 12y = 96

__24x – 8y = 16__

20y = 80

Y=4

Substitute for y in eqn 1

4x + 2(4) =16; 4x +8 =16

4x =16 -8; 4x=8; x=2

Therefore, y-x=4-2=2

**14. **Given that R is directly proportional to L and inversely proportional to P, R=3 when L =9 and P=0.8, find R when L=15 and P =1.8

**A.**2.2**B.**3.3**C.**6.6**D.**0.3

**Correct Option: Answer is A**

**15. **** **

In the diagram, angle ABC and angle BCD are right angles, angle BAD = t and angle EDF = 70^{o}, find the value of t.

**A.**70\(^o\)**B.**165\(^o\)**C.**140\(^o\)**D.**110\(^o\)

**Correct Option: Answer is D**

opp angles are equal ∠CDE = 70°

Sum of interior angles in a quadrilateral = 360°

(90 + 90 + 70 + t)° = 360°

t° = 360° – 250°

t° = 110°