Q. The average of 30 numbers is 15. The average of the first 18 number is 10 and that of next 11 numbers is 20. The last number is :
Answer: 50
Notes: Let the last number be x. According to the question, 18 $latex \times$ 10 + 11 $latex \times$ 20 + x = 30 $latex \times$ 15 => 180 + 220 + x = 450 => 400 + x = 450 => x = 450 - 400 = 50 Hence option [A] is correct answer.

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