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UPSC Prelims

Mathematics

Theme:

Number System / संख्या पद्धति

Q45 2017, Number System

There are thirteen 2-digit consecutive odd numbers. If 39 is the mean of the first five such numbers, then what is the mean of all the thirteen numbers?

तेरह 2-अंकीय, क्रमागत विषम संख्याएँ हैं। यदि ऐसी पहली पाँच संख्याओं का माध्य 39 है, तो सभी तेरह संख्याओं का माध्य क्या है?

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These are consecutive odd numbers. The mean of the first 5 such numbers will be third such number, which is given to be as 39.

Hence, the series is: 35, 37, 39, 41, 43, 45, 47, 49, 51 and so on.

Now, mean of all the thirteen numbers = {[(13 -1)/2] + 1} th term = 7th term from the start, i.e. 47.

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