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The following question it puts forth you:
25 - 55 + (85 + 65) = ?
Then, you are told that even though you might think its wrong, the correct answer is actually 5!
Whats your reaction to it? How can this be true?
That's how it's perfectly correct!
Why it was looking wrong?
If you read the data carefully then you will notice '!' attached to number 5 which is being claimed answer. Actually claimed answer is 5! not 5 Read it again...
"Then, you are told that even though you might think its wrong, the correct answer is actually 5!."
Now use of '!' is not limited to the sentences only. In mathematics it's a 'factorial'.
So 5! = 5 x 4 x 3 x 2 x 1 = 120 and 25 - 55 + (85 + 65) = 120 and hence,
25 - 55 + (85 + 65) = 5!
Now doesn't it look the correct equation?
In a competitive exam, each correct answer could win you 10 points and
each wrong answer could lose you 5 points. You sat in the exam and
answered all the 20 questions, which were given in the exam.
When you checked the result, you had scored 125 marks in the test.
Can you calculate how many answers given by you were correct and wrong ?
These should be those numbers!
What was the test ?
Let C be the number of correct answers and W be the number of wrong answers.
Since there are 20 question in total,
C + W = 20 .....(1)
and the score 125 must be subtraction of marks obtained for correct answer and marks due to wrong answers.
10C - 5W = 125 .....(2)
Multiplying (1) by 5 and then adding it to (2),
5C + 5W + 10C - 5W = 100 + 125
15C = 225
C = 15.
From (1), W = 20 - C = 20 - 5 = 5.
Hence, your 15 answers are correct while 5 answers are wrong.
