WAEC Mathematics Past Questions & Answers - Page 158

786.

If 8x-1 = \(\frac{1}{4}\), find x

A.

-\(\frac{-5}{3}\)

B.

-1

C.

-\(\frac{1}{3}\)

D.

\(\frac{1}{3}\)

Correct answer is D

8x-1 = \(\frac{1}{4}\)

23(x - 1 = 2-2

3x - 3 = -2

3x = -2 + 3

3x = 1

x = \(\frac{1}{3}\)

787.

Solve the simultaneous equations x + y = 2 and 3x - 2y = 1

A.

x = 2 and y = 1

B.

x = 1 and y = 1

C.

x = 1 and y = 2

D.

x = -1 and y = 1

Correct answer is B

x + y = 2........... (i)

3x - 2y = 1......(ii)

From (i): x = 2 - y ..........(iii)

subt. (2 - y) for x in (ii)

3(2 - y) 2y = 1

6 - 3y - 2y = 1

-5y = 1 - 6 = -5

y = \(\frac{-5}{-5}\) = 1

subst. (i) for y in (iii)

x = 2 - 1 = 1

x = 1, y = 1

788.

If x = 3, Y = 2 and z = 4, what is the value of 3x2 - 2y + z?

A.

17

B.

27

C.

35

D.

71

Correct answer is B

x = 3, y = 2, z = 4

3x2 - 2y + z

= 3(3)2 - 2(2) + 4

3(9) - 4 + 4 = 27

789.

For what value of x is the expression \(\frac{2x - 1}{x + 3}\) not defined?

A.

3

B.

2

C.

\(\frac{1}{2}\)

D.

-3

Correct answer is D

\(\frac{2x - 1}{x + 3}\) not defined

x + 3 = 0

x = -3

790.

I am x years old and my brother is 3 years older. How old was my brother last year?

A.

(x - 4)years

B.

(x + 2) years

C.

(3x - 10years

D.

(3x + 1)years

Correct answer is B

I am x years old; My brother = 3 + x; My brother

last year = (3 + x) - 1 = x + 3 - 1

= (x + 2) years