Reasoning - Mathematical Operations

This is a part of reasoning section where the questions are based upon the normal and basic mathematical operations but not in the same procedure. It means that there will be certain manipulation with the symbols of the operator and the reader needs to solve those questions keeping in mind those manipulations. For example, it will be given to consider + as – then you have to perform subtraction at the point of + symbol.

Not only mathematical operators, but also there can be change in operands too. For example if there is section “5 + 2/3 - 7” and the reader is asked to solve that by replacing + as - and 5 as 7 then the sequence will be “7 - 2/3 + 5”. Our understanding will be clearer once we go through a sample problem.

Example-1

Directions for questions − If

‘+’ = ’×’

‘-‘ = ’+’

‘×’ = ’/’

’/’ = ‘-‘

Then answer the following questions based on this information

1. 23 - 3/1 + 15 × 5 =

A - 22

B - 23

C - 24

D - 25

Explanation −

If the actual operators will be replaced as per the direction of the question, then the series will be −

23 + 3 - 1 × 15/5

Now we can apply the rule to solve the above. 1st “15/5” section will be solved.

15/5=3

Now (1 × 3) section will be solved.

1 × 3 = 3

Series will reduce to 23 + 3 - 3 = 23

Hence our answer will be option B.

Give interchanges −

Signs + and / and numbers 2 and 3

Example-2

A - 3/18 - 2 + 1 = 17

B - 3/20 - 2 + 1 = 16

C - 20/3 - 2 + 1 = 17

D - 20/3 - 2 + 1 = 16

Answer - Option A

Explanation −

Here we can see the question has asked us to interchange the sign of + with / and vice versa. Similarly we have to also interchange the numbers 2 and 3. If we go on solving option A −

LHS −

3/18 - 2 + 1 (Given)

2 + 18 - 3/1 (After Interchange)

Now solving the above we will get 17 = RHS

But if we will go on others solving like this we will not get correct RHS.

Example-3

A - 3/23 - 13 + 13 = 10

B - 13/13 - 3 + 23 = 21

C - 13/13 - 23 + 3 = - 21

D - 3/23 - 13 + 13 = 1

Answer − Option D

Explanation −

Without interchanging the sign if we solve the problem, our answer will be option C. However; if we will interchange the sign as suggested in the previous example and will go on solving rest of the options, then we can observe that only option D will satisfy the criteria. Hence; option D will be our answer over here.