JAMB Mathematics Past Questions & Answers - Page 260

1,297.

The probability of an event P is \(\frac{3}{4}\) while that of another event Q is \(\frac{1}{6}\). If the probability of both P and Q is \(\frac{1}{2}\). What is the probability of either P or Q.

A.

\(\frac{1}{96}\)

B.

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

C.

\(\frac{5}{6}\)

D.

\(\frac{11}{12}\)

Correct answer is D

Prob of P = \(\frac{3}{4}\)

Prob of Q = \(\frac{1}{6}\)

Prob of both P or Q = \(\frac{3}{4} + \frac{1}{6} = \frac{11}{12}\)

1,298.

Two perfect dice are thrown together, Determine the probability of obtaining a total score of 8

A.

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

B.

\(\frac{5}{36}\)

C.

\(\frac{1}{6}\)

D.

\(\frac{7}{36}\)

Correct answer is B

\(\begin{array}{c|c} & & 1 & 2 & 3 & 4 & 5 & 6 \\ \hline a & 1 & 1, 1 & 1, 2 & 1, 3 & 1, 4 & 1, 5 & 1, 6\\\hline & 2 & 1,1 & 2, 2 & 2, 3 & 2, 4 & 2, 5 & 2, 6 \\\hline B & 3 & 3, 1 & 3, 2 & 3, 3 & 3, 4 & 3, 5 & 3, 6\\\hline & 4 & 4 , 1 & 4, 2 & 4, 3 & 4, 4 & 4, 5 & 4, 6\\\hline Die & 5 & 5, 1 & 5, 2 & 5, 3 & 5, 4 & 5, 5 & 5, 6 \\\hline & 6 & 6, 1 & 6, 2 & 6, 3 & 6, 4 & 6, 5 & 6, 6\end{array}\)

Probability of obtaining total score of 8 = \(\frac{5}{36}\)

1,299.

If the scores of 3 students in a test are 5, 6 and 7, find the standard deviation of their scores

A.

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

B.

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

C.

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

D.

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

Correct answer is C

(x) = \(\frac{5 + 6 + 7}{3}\)

= \(\frac{18}{3}\)

= 6

\(\begin{array}{c|c} scores(X) & \text{d = (x - x) deviation} & (deviation)^2\\\hline 5 & 5 - 6 & 1\\ 6 & 6 - 6 & 0 \\ 7 & 7 - 6 & 1\\ \hline & & 2\end{array}\)

S.D \(\sqrt{\frac{\sum d^2}{n}}\) where d = deviation = (x - x)

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