JAMB Mathematics Past Questions & Answers - Page 178

886.

A sum of money invested at 5% per annum simple interest amounts to $285.20 after 3 years. How long will it take the same sum to amount to $434.00 at 7\(\frac{1}{2}\)% per annum simple interest?

A.

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

B.

10 years

C.

5 years

D.

12 years

E.

14 years

Correct answer is B

\(A = P(1 + \frac{R}{100})^{T}\)

\(285.20 = P(1 + \frac{5}{100})^{3}\)

\(285.20 = P(1.05)^{3} \implies 1.16P = 285.20\)

\(P = \frac{285.20}{1.16} = $245.86\)

Given Amount = $434.00

Interest = Amount - Principal

Interest = $434.00 - $245.86 = $188.14

\(T = \frac{100I}{PR}\)

\(T = \frac{100 \times 188.14}{245.86 \times 7.5}\)

\(T = \frac{18814}{1843.95} = 10.2\)

Approximately 10 years.

887.

7 pupils of average age 12 years leave a class of 25 pupils of average age 14 years. If 6 new pupils of average age 11years join the class, what is the average age of the pupils now in the class?

A.

13years

B.

12 years 7\(\frac{1}{2}\) months

C.

13 years 5 months

D.

13 years 10 months

E.

11 years

Correct answer is D

Total age of the 7 pupils = 7 x 12 = 84

Total age of the 25 pupils = 25 x 14 = 350

Total age of the 6 pupils = 6 x 11 = 66

7 pupils leaving a class of 25 pupils given 18 pupils

Total age of the 18 pupils = 350 - 84 = 266

6 pupils joining 18 pupils = 24

Total age of 24 pupils = 266 + 66 = 332

Average age of 24 pupils now in class \(\frac{332}{24}\)

= 13yrs 10 months

888.

If \(\sin x° = \frac{a}{b}\), what is \(\sin (90 - x)°\)?

A.

\(\frac{\sqrt{b^2 - a^2}}{b}\)

B.

1\(\frac{-a}{b}\)

C.

\(\frac{b^2 - a^2}{b}\)

D.

\(\frac{a^2 - b^2}{b}\)

E.

\(\sqrt{b^2 - a^3}\)

Correct answer is A

\(\sin x = \frac{a}{b}\)

\(\sin^{2} x + \cos^{2} x = 1\)

\(\sin^{2} x = \frac{a^{2}}{b^{2}}\)

\(\cos^{2} x = 1 - \frac{a^{2}}{b^{2}} = \frac{b^{2} - a^{2}}{b^{2}}\)

\(\therefore \cos x = \frac{\sqrt{b^{2} - a^{2}}}{b}\)

\(\sin (90 - x) = \sin 90 \cos x - \cos 90 \sin x\)

= \((1 \times \frac{\sqrt{b^{2} - a^{2}}}{b}) - (0 \times \frac{a}{b})\)

= \(\frac{\sqrt{b^{2} - a^{2}}}{b}\)

889.
890.

Marks scored by some children in an arithmetic test are:5, 3, 6, 9, 4, 7, 8, 6, 2, 7, 8, 4, 5, 2, 1, 0, 6, 9, 0, 8.
The arithmetic mean of the marks is

A.

6

B.

5

C.

8

D.

7

E.

10

Correct answer is B

Add all the No.s together to give 100

\(\sum\)xf = 100

N = 20

x = \(\frac{\sum xf}{N}\)

= \(\frac{100}{20}\)

= 5