JAMB Mathematics Past Questions & Answers - Page 268

1,336.

What is the value of x satisfying the equation \(\frac{4^{2x}}{4^{3x}}\) = 2?

A.

-2

B.

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

C.

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

D.

2

Correct answer is B

\(\frac{4^{2x}}{4^{3x}}\) = 2

42x - 3x = 2

4-x = 2

(22)-x

= 21

Equating coefficients: -2x = 1

x = -\(\frac{1}{2}\)

1,337.

Evaluate \(\log_{b} a^{n}\) if \(b = a^{\frac{1}{n}}\).

A.

n2

B.

n

C.

\(\frac{1}{n}\)

D.

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

Correct answer is A

Let \(\log_{b} a^{n} = x\)

\(\therefore a^{n} = b^{x}\)

\(a^{n} = (a^{\frac{1}{n}})^{x}\)

\(a^{n} = a^{\frac{x}{n}} \implies n = \frac{x}{n}\)

\(x = n^{2}\)

1,338.

The radius of a circle is given as 5cm subject to an error of 0.1cm. What is the percentage error in the area of the circle?

A.

\(\frac{1}{25}\)

B.

\(\frac{1}{4}\)

C.

4

D.

25

Correct answer is C

% error in Area = \(\frac{\pi(5.1)^2 - \pi(5)^2 \times 100%}{\pi(5)^2}\)

= \(\frac{\pi 26.01 - 25 \times 100%}{\pi(25)}\)

= \(\frac{1.01}{25}\) x 100%

= 4.04%

1,339.

Find n if 34n = 100112

A.

5

B.

6

C.

7

D.

8

Correct answer is A

To find n if 34n = 100112, convert both sides to base 10

= 3n + 4 = (1 x 24) + (0 x23) + (0 x 22) + (1 x 21) + 1 x 2o

= 3n + 4 = 16 + 0 + 0 + 2 + 1

3n + 4 = 19

3n = 15

n = 5

1,340.

The chances of three independent events X, Y, Z occurring are \(\frac{1}{2}\), \(\frac{2}{3}\), \(\frac{1}{4}\) respectively. What are the chances of Y and Z only occurring?

A.

\(\frac{1}{8}\)

B.

\(\frac{1}{24}\)

C.

\(\frac{1}{12}\)

D.

\(\frac{1}{4}\)

Correct answer is C

Chance of x = \(\frac{1}{2}\)

Change of Y = \(\frac{2}{3}\)

Chance of Z = \(\frac{1}{4}\)

Chance of Y and Z only occurring

= Pr (Y ∩ Z ∩ Xc)

where Xc = 1 - Pr(X)

1 - \(\frac{1}{2}\) = \(\frac{1}{2}\)

= Pr(Y) x Pr(Z) x Pr(Xc)

= \(\frac{2}{3}\) x \(\frac{1}{4}\) x \(\frac{1}{2}\)

= \(\frac{1}{12}\)