Question
There are 15 numbers such that average of first 12
numbers is 65 while the average of last five numbers is 76. Find the 12th number, if the ratio between 11th and 12th number is 13:7, respectively.Solution
Avg of first 12 numbers = 65 → Sum = 12 × 65 = 780 Avg of last 5 numbers = 76 → Sum = 5 × 76 = 380 11th : 12th = 13 : 7 → Let 11th = 13x, 12th = 7x → 11th + 12th = 20x So, Sum of 1st to 10th = 780 − 20x No further info to find x ⇒ 12th = 7x can’t be calculated Hence, Can’t be determined (not enough data)
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