7th Class Mental Ability Mathematical Reasoning Mathematical Operations

There are four fundamental operations.

These are addition\[\left( + \right)\], subtraction\[\left( - \right)\], multiplication \[\left( \times  \right)\]and division\[\left( \div  \right)\].

Whenever two or more of these operations occur simultaneously, we overcome on such complex situation by applying the "B O D M A S' rule.

This chapter is on the basis of the 'B O D M A S' rule. Let us explain this rule briefly.

B \[\to \] Bracket, P \[\to \] Of, D \[\to \] Division, M \[\to \] Multiplication, A \[\to \] Addition, S \[\to \] Subtraction

We solve an expression first for 'bracket' (if available), then for 'of (if available).

This process goes up to subtraction.

EXAMPLE

Which one of the following interchanges in signs and numbers would make the equation \[3+7\times 4=25\] true?                   

(a) \[3\text{ }and\text{ }4,+\,and\times ~~\]                               

(b) \[3\text{ }and\text{ }7,+\text{ }and\text{ }x\]

(c) \[4\text{ }and\text{ }7,+\text{ }and\text{ }\times ~\]                           

(d) None of these

Explanation (b):

Let us consider option (b)

\[3+7\times 4=25\] becomes \[7\times 3+4=25\]

or 21 + 4 = 25 or 25 = 25, which is true.

So, the correct option is (b).