JAMB Mathematics Past Questions & Answers - Page 284

1,416.

Solve for x if \(25^{x} + 3(5^{x}) = 4\)

A.

1 or -4

B.

0

C.

1

D.

-4 or 0

Correct answer is B

\(25^{x} + 3(5^{x}) = 4\)

Let \(5^{x}\) = y.

\((5^{2})^{x} + 3(5^{x}) - 4 = 0\)

\(y^{2} + 3y - 4 = 0\)

\(y^{2} - y + 4y - 4 = 0\)

\(y(y - 1) + 4(y - 1) = 0\)

\((y + 4)(y - 1) = 0\)

\(y = -4 ; y = 1\)

y = -4 is not possible.

y = 1 \(\implies\) x = 0.

1,417.

A die has four of it's faces coloured white and the remaining two coloured black. What is the probability that when the die is thrown two consecutive time, the top face will be white in both cases?

A.

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

B.

\(\frac{1}{9}\)

C.

\(\frac{4}{9}\)

D.

\(\frac{1}{36}\)

Correct answer is C

\(\begin{array}{c|c} & W & W & W & W & B & B \\ \hline W & WW & WW & WW & WW & WB & WB \\ W & WW & WW & WW & WW & WB & WB\\W & WW & WW & WW & WW & WB & WB\\ W & WW & WW & WW & WW & WB & WB\\ B & BW & BW & BW & BW & BB & BB \\ B & BW & BW & BW & BW & BB & BB\end{array}\)

P(WW) = \(\frac{16}{36}\)

= \(\frac{4}{9}\)

1,418.

Let p be a probability function on set S, where S = (a1, a2, a3, a4). Find P(a1) if P(a2) = \(\frac{1}{3}\), p(a3) = \(\frac{1}{6}\) and p(a4) = \(\frac{1}{5}\)

A.

\(\frac{7}{3}\)

B.

\(\frac{2}{3}\)

C.

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

D.

\(\frac{3}{10}\)

Correct answer is D

No explanation has been provided for this answer.