The average of 30 numbers is 1.2. The average of the first 20 of them is 1.1 and that of the next 9 is 1. Then the last number is:

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  1. 4.9
  2. 4
  3. 5
  4. 4.6

Answer (Detailed Solution Below)

Option 3 : 5
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Detailed Solution

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Given:

Average of 30 numbers = 1.2

Average of first 20 numbers = 1.1

Average of next 9 numbers = 1

Formula used:

Sum = Average × Number of terms

Calculation:

Sum of 30 numbers = 1.2 × 30 = 36

Sum of first 20 numbers = 1.1 × 20 = 22

Sum of next 9 numbers = 1 × 9 = 9

Last number = Total sum - (Sum of first 20 + Sum of next 9)

⇒ Last number = 36 - (22 + 9)

⇒ Last number = 36 - 31

⇒ Last number = 5

∴ The last number is 5.

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