JAMB Mathematics Past Questions & Answers - Page 280

1,396.

Solve for x and y \(\begin{pmatrix} 1 & 1 \\ 3 & y \end{pmatrix}\)\(\begin{pmatrix} x \\ 1 \end{pmatrix}\) = \(\begin{pmatrix} 4 \\ 1\end{pmatrix}\)

x = 3, y = 8

x = 3, y = -8

x = -8, y = 3

x = 8, y = -3

View answer & explanation

Correct answer is B

\(\begin{pmatrix} 1 & 1 \\ 3 & y \end{pmatrix}\)\(\begin{pmatrix} x \\ 1 \end{pmatrix}\) = \(\begin{pmatrix} 4 \\ 1\end{pmatrix}\) = x + 1 = 4

x = 4 - 1

= 3

3x + y =1

3(3) = y = 1

= 9 + y = 1

y = 1 - 9

= -8

1,397.

\(\begin{array}{c|c} \oplus mod 10 & 2 & 4 & 6 & 8 \\ \hline 2 & 4 & 8 & 2 & 6 \\4 & 8 & 6 & 4 & 2\\ 4 & 8 & 6 & 4 & 2\\ 6 & 2 & 4 & 6 & 8\\ 8 & 6 & 2 & 8 & 4\end{array}\)
The multiplication table above has modulo 10 on the set S = (2, 4, 6, 8). Find the inverse of 2

View answer & explanation

Correct answer is A

The inverse of 2 is 6 since 2 x 6 = 12; under mod 10

12 = 2 which is also the value required

1,398.

A binary operation \(\oplus\) is defines on the set of all positive integers by a \(\oplus\) b = ab for all positive integers a, b. Which of the following properties does NOT hold?

closure

identity

positive

inverse

View answer & explanation

Correct answer is D

a \(\oplus\) b = ab

The set of all national rules Q, is closed under the operations, additions, subtraction, multiplication and division. Since a \(\oplus\) b = ab; b \(\oplus\) a = ba = ab

The number 1 is the identity element under multiplication

1,399.

Find the nth term of the sequence 3, 6, 10, 15, 21.....

\(\frac{n(n - 1)}{2}\)

\(\frac{n(n + 1)}{2}\)

\(\frac{(n + 1)(n + 2)}{2}\)

n(2n + 1)

View answer & explanation

Correct answer is C

\(\frac{(n + 1)(n + 2)}{2}\)

If n = 1, the expression becomes 3

n = 2, the expression becomes 6

n = 4, the expression becomes 15

n = 5, the expression becomes 21