New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    The average of twelve numbers is 45.5. The average of

    the first four numbers is 41.5 and that of the next five numbers is 48. The 10th number is 4 more than the 11th number and 9 more than the 12th number. What is the average of the 10th and 12th numbers?
    A 47 Correct Answer Incorrect Answer
    B 46.5 Correct Answer Incorrect Answer
    C 46 Correct Answer Incorrect Answer
    D 47.8 Correct Answer Incorrect Answer

    Solution

    Average of 12 numbers = 45.5 Sum of 12 numbers = 45.5 × 12 = 546 Average of first 4 numbers = 41.5 Sum of first 4 numbers = 41.5 × 4 = 166 Average of next 5 numbers = 48 Sum of next 5 numbers = 48 × 5 = 240 Sum of 10th, 11th and 12th number = 546 – 166 – 240 = 140 Let the 10th number be x. 11th number = x – 4 12th number = x – 9 According to the question, => x + x – 4 + x – 9 = 140 ⇒ 3x – 13 = 140 ⇒ 3x = 140 + 13 ⇒ 3x = 153 ∴ x = 153/3 = 51 Average of 10th and 12th number = (51 + 51 – 9)/2 = 93/2 = 46.5

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