WAEC Mathematics Past Questions & Answers - Page 26

126.

The height of an equilateral triangle of side is 10 3√ cm. calculate its perimeter.

A.

20cm

B.

60cm

C.

40cm

D.

30cm

Correct answer is B

Height of an equilateral triangle, h = a\(\frac{√3}{2}\), where a is the side of the equilateral triangle.

10√3 = a\(\frac{√3}{2}\)

cross multiply--> 2 * 10√3 = a√3

√3 strikes √3 on both sides

20 = a

The perimeter of an equilateral triangle is: P = 3a

P = 3 * 20 = 60cm

P = 30√3

127.

A trader paid import duty of 38 kobo in the naira on the cost of an engine. If a total of #22,800.00 was paid as import duty, calculate the cost of the engine.

A.

#60,000.00

B.

#120,000.00

C.

#24,000.00

D.

#18,000.00

Correct answer is A

No explanation has been provided for this answer.

128.

make u the subject in x =\(\frac{2u-3}{3u + 2}\)

A.

u = \(\frac{2x + 3}{3x - 2}\)

B.

u = \(\frac{2x - 3}{3x - 2}\)

C.

u = \(\frac{2x + 3}{2 - 3x}\)

D.

u = \(\frac{2x + 3}{3x + 2}\)

Correct answer is C

x =\(\frac{2u-3}{3u + 2}\)

cross multiply

x(3u + 2) = 2u - 3

3ux + 2x = 2u - 3

collect like terms of u

2x + 3 = 2u - 3ux 

\(\frac{2x + 3}{2 - 3x}\) = u

129.

The sum of the interior angles of a regular polygon with k sides is (3k-10) right angles. Find the size of the exterior angle?

A.

60°

B.

40°

C.

90°

D.

120°

Correct answer is A

In a polygon with n sides, the sum of the angles =

(n - 2)180, where n = the number of sides.

In our problem, n = k.

So, we have:

(3k - 10)90 = (k - 2)180

270k - 900 = 180k - 360

Simplifying:

90k = 540

k = 6. So, we have a regular hexagon.

Now, each exterior angle = 360/n

We have: 360/6 = 60

Conclusion: Each exterior angle is 60 degrees.

130.

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

A.

8

B.

2

C.

4

D.

6

Correct answer is B

Using elimination method:

4x+2y=16 * 6 --> 24x +12y=96 ... eqn iii

6x-2y=4  * 4 --> 24x - 8y = 16 ... eqn iv

Subtract eqn iv from iii

20y = 80

y = 4

Subst. y for 4 in 4x + 2y = 16

--> 4x + 2(4) = 16

--> 4x = 16 - 8

--> 4x = 8

--> x = 2

: The value of (y-x) is 4 - 2 = 2