Question
Download Solution PDFThe average of nine numbers is 60, that of the first five numbers is 55 and the next three is 65. The ninth number is 10 less than the tenth number. Then, tenth number is –
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFGiven:
Average of nine numbers = 60
Average of first five numbers = 55 and average of next three numbers = 65
Tenth number = Ninth number + 10
Concept used:
Average = Total sum of all numbers / (Count of the numbers)
Calculation:
The sum of nine numbers = 60 × 9 = 540
The sum of the first five numbers = 55 × 5 = 275
The sum of the next three numbers = 65 × 3 = 195
Ninth number = (540 – 275 – 195) = (540 – 470) = 70
∴ Tenth number = 70 + 10 = 80
Mistake PointsWe have details about 10 numbers but the average is given only of 9
numbers. To calculate the 10th number, we have a relationship that is
the ninth number is 10 less than the tenth number. So after calculating
the 9th number, use this relation to find the next number. Don't take
the average of 10th number.
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