CSAT 2024

Q. If a+b means a-b; a-b means axb; axb means a÷b; a÷b means a+b, then what is the value of 10+30-100 x 50÷25? (Operations are to be replaced simultaneously)

a) 15
b) 0
c) -15
d) -25
Correct answer: d) -25

Question from UPSC Prelims 2024 CSAT

Explanation : 

Original Expression:
10 + 30 – 100 x 50 / 25

Replacing each operator simultaneously:
The plus sign (+) becomes minus (-)
The minus sign (-) becomes multiply (x)
The multiply sign (x) becomes divide (/)
The divide sign (/) becomes plus (+)

After replacing all operators at once, the expression becomes:
10 – 30 x 100 / 50 + 25

Now let’s solve this expression following standard order of operations:

First step: Work out multiplication
30 x 100 equals 3000

Second step: Work out division
3000 / 50 equals 60

Third step: The expression is now
10 – 60 + 25

Fourth step: Work from left to right with subtraction and addition
10 minus 60 equals -50
-50 plus 25 equals -25

Therefore, the final answer is -25

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