JAMB Mathematics Past Questions & Answers - Page 52

256.

If 2\(^{x + y}\) = 16 and 4\(^{x - y} = \frac{1}{32}\), find the values of x and y.

A.

x = \(\frac{3}{4}\), y = \(\frac{11}{4}\)

B.

x = \(\frac{3}{4}\), y = \(\frac{13}{4}\)

C.

x = \(\frac{2}{3}\), y = \(\frac{4}{5}\)

D.

x = \(\frac{2}{3}\), y = \(\frac{13}{4}\)

Correct answer is B

2\(^{x + y}\) = 16 ; 4\(^{x - y}\) = \(\frac{1}{32}\).

\(\implies 2^{x + y} = 2^4\)

\(x + y = 4 ... (1)\)

\(2^{2(x - y)} = 2^{-5} \)

\(2^{2x - 2y} = 2^{-5}\)

\(\implies 2x - 2y = -5 ... (2)\)

Solving the equations (1) and (2) simultaneously, we have

x = \(\frac{3}{4}\) and y = \(\frac{13}{4}\)

257.

If 2\(^{x + y}\) = 16 and 4\(^{x - y} = \frac{1}{32}\), find the values of x and y

A.

x = \(\frac{3}{4}\), y = \(\frac{11}{4}\)

B.

x = \(\frac{3}{4}\), y = \(\frac{13}{4}\)

C.

x = \(\frac{2}{3}\), y = \(\frac{4}{5}\)

D.

x = \(\frac{2}{3}\), y = \(\frac{13}{4}\)

Correct answer is B

2\(^{x + y}\) = 16 ; 4\(^{x - y}\) = \(\frac{1}{32}\).

\(\implies 2^{x + y} = 2^4\)

\(x + y = 4 ... (1)\)

\(2^{2(x - y)} = 2^{-5} \)

\(2^{2x - 2y} = 2^{-5}\)

\(\implies 2x - 2y = -5 ... (2)\)

Solving the equations (1) and (2) simultaneously, we have

x = \(\frac{3}{4}\) and y = \(\frac{13}{4}\)

258.

Evaluate \((\frac{6}{0.32} \div \frac{2}{0.084})^{-1}\) correct to 1 decimal place.

A.

1.3

B.

2.5

C.

4.6

D.

3.2

Correct answer is A

\((\frac{6}{0.32} \div \frac{2}{0.084})^{-1}\)

= \((\frac{600}{32} \div \frac{2000}{84})^{-1}\)

= \((\frac{600}{32} \times \frac{84}{2000})^{-1}\)

= \((\frac{63}{80})^{-1}\)

= \(\frac{80}{63}\)

= 1.3 (to 1 decimal place)

259.

The weight of a day-old chick was measured to be 0.21g. If the actual weight of the chick is 0.18g, what was the percentage error in the measurement?

A.

15.5%

B.

18.2%

C.

14.8%

D.

16.7%

Correct answer is D

Actual weight = 0.18g

Error = 0.21g - 0.18g

= 0.03g

% error = \(\frac{0.03}{0.18} \times 100%\)

= 16.7%

260.

The angles of a polygon are given by 2x, 5x, x and 4x respectively. The value of x is

A.

31°

B.

30°

C.

26°

D.

48°

Correct answer is B

Since there are 4 angles given, the polygon is a quadrilateral.

Sum of angle in a quadrilateral = 360°

∴∴ 2x + 5x + x + 4x = 360°

12x = 360°

x = 30°