WAEC Mathematics Past Questions & Answers - Page 272

1,356.

A 120° sector of a circle of radius 21cm is bent to form a cone. What is the base radius of the cone?

A.

31/2cm

B.

7cm

C.

1O1/2cm

D.

14cm

E.

21cm

Correct answer is B

The length of the arc subtended by the sector of angle 120° = circumference of the base of the cone.

\(\frac{120}{360} \times 2 \times \frac{22}{7} \times 21 = 2\pi r\)

\(44 = 2\pi r\)

\(r = 22 \div \pi\)

\(r = 22 \times \frac{7}{22}\)

r = 7 cm

1,357.

The positions of two countries P and Q are (15°N, 12°E) and (65°N, 12°E) respectively. What is the difference in latitude?

A.

104o

B.

100o

C.

80o

D.

50o

E.

24o

Correct answer is D

Latitudinal difference = 65° - 15° 

= 50°

1,358.

The diagram above shows a cone with the dimensions of its frustrum indicated. Calculate the height of the cone.

A.

12cm

B.

15cm

C.

18cm

D.

24cm

E.

30cm

Correct answer is D

Considering the smaller and larger triangle, these two are similar triangles. Hence, 

If the height of the smaller triangle = h, 

\(\therefore \frac{h}{6} = \frac{h + 12}{12}\)

\(12h = 6h + 72 \implies 6h = 72\)

\(h = 12 cm\)

\(\therefore\) The height of the cone = 12 + 12 = 24 cm

1,359.

A hollow sphere has a volume of kcm3 and a surface area of kcm2. Calculate the diameter of the sphere.

A.

3cm

B.

6cm

C.

9cm

D.

12cm

E.

More information is needed

Correct answer is B

\(Volume = \frac{4}{3} \pi r^3 = k\) ...(i)

\(S.A = 4\pi r^2 = k\) ... (ii)

Divide (i) by (ii),

\(\frac{4}{3} \pi r^3 \div 4\pi r^2 = \frac{k}{k}\)

\(\frac{r}{3} = 1 \implies r = 3cm\)

Diameter = 2 x 3cm = 6cm

1,360.

Find the total surface area of solid circular cone with base radius 3cm and slant height 4cm. [Take π = 22/7]

A.

37 5/7cm2

B.

66cm2

C.

75 3/7cm2

D.

78 2/7cm2

E.

88cm2

Correct answer is B

T.S.A of a cone = \(\pi r^2 + \pi rl\)

= \(\frac{22}{7} \times 3^2 + \frac{22}{7}  \times 3 \times 4\)

= \(\frac{198}{7} + \frac{264}{7}\)

= \(\frac{462}{7}\)

= 66 cm\(^2\)