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JAMB Mathematics 2019 Paper

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Question : 3

Total: 73

A binary operation

\otimes

m \otimes n = mn + m - n

on the set of real numbers, for all m, n

\in

R. Find the value of 3

\otimes

\otimes

4).

6
25
15
18

Solution:

Concept:

Use the given binary operation rule

m \otimes n = mn + m - n

and evaluate from the inside bracket first.

Explanation:

First, compute the bracket:

2 \otimes 4

.

Substitute

m = 2

and

n = 4

into the formula:

2 \otimes 4 = (2)(4) + 2 - 4 = 8 + 2 - 4 = 6.

Now evaluate

3 \otimes (2 \otimes 4) = 3 \otimes 6

.

Substitute

m = 3

and

n = 6

:

3 \otimes 6 = (3)(6) + 3 - 6 = 18 + 3 - 6 = 15.

Thus, the value is

15

.

Answer:

C. 15

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