Question
The average of 16 numbers is 20. The average of 1st 7
numbers is 15 and the average of the last 7 numbers is 25. The 8th number is 16 more than the 9th number. What is the value of the 8th and 9th numbers?Solution
Let the 8th and 9th numbers be x and y respectively. Sum of 16 number = 16 × 20 = 320 Sum of first 7 number = 7 × 15 = 105 Sum of last 7 number = 7 × 25 = 175 ATQ: x + y = 320 - 105 - 175 x + y = 40 We know that: x = 16 + y so, 16 + y + y = 40 2y = 40 - 16 = 24 y = 12 then, x = 16 + 12 = 28
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