JAMB Mathematics Past Questions & Answers - Page 157

781.

A father is now three times as old as his son. Twelve years ago he was six times as old as his son. How old are the son and the father?

A.

20 and 45

B.

100 and 150

C.

45 and 65

D.

35 and 75

E.

20 and 60

Correct answer is E

Son = x, Father = 3x, 12 yrs ago

son = x - 12, father = 3x - 12

3x - 12 = 6(x - 12)

3x - 12 = 6x - 72

3x = 60

x = 20

782.

If y = x2 - 2x - 3, Find the least value of y and corresponding value of x

A.

x = 3, y = 3

B.

x = 1, y = -3

C.

x = 4, y = 1

D.

x = 1, y = -4

E.

x = 2, y = -3

Correct answer is D

If the graph of eqn. y = x2 - 2x - 3 is plot and drawn, the lease value of y = -4 while the corresponding value of x = 1

x = 1, y = -4

783.

The following table relates the number of objects f corresponding to a certain size x. What is the average size of an object?
\(\begin{array}{c|c} f & 1 & 2 & 3 & 4 & 5 \\ \hline x & 1 & 2 & 4 & 8 & 16\end{array}\)

A.

\(\frac{31}{15}\)

B.

\(\frac{31}{5}\)

C.

\(\frac{129}{5}\)

D.

\(\frac{43}{5}\)

E.

\(\frac{16}{5}\)

Correct answer is D

F = 1, 2, 3, 4, 5

x = 1, 2, 4, 8, 16

fx = 1, 4, 12, 32, 80, 3f = 15

(average size) = \(\frac{\sum fx}{\sum f}\)

= \(\frac{129}{15}\)

= \(\frac{43}{5}\)

784.

The size of a quantity first doubles and then increases by a further 16%. After a short time its size decreases by 16%. What is the net increases in size of the quantity?

A.

\(\frac{59300}{625}\)

B.

\(\frac{50900}{625}\)

C.

200%

D.

+100%

Correct answer is C

Let x rept. the size of the quantity

2x + \(\frac{116}{100}\) x \(\frac{-84}{100}\)

= 200%

785.

What is log7(49a) - log10(0.01)?

A.

\(\frac{49^a}{100}\)

B.

\(\frac{a}{2}\) + 2

C.

72a + 2

D.

2a + 2

E.

\(\frac{2a}{2}\)

Correct answer is D

log7(49a) - log10(0.01) = log7(72)a - log10100

log772a - log101 - log10 102

= 2a - 2

= 2a + a