- 34
- 42
- 30
- 26
- 39

Option 3 : 30

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Let the sum of seven numbers is x

⇒ Average = x/7 = 24

⇒ x = 168

Let, sum of first six numbers is y

⇒ y/6 = 21

⇒ y = 126

⇒ Last number = 168 – 126 = 42

⇒ Twice of last number = 42 × 2 = 84

Now, the sum of 7 numbers become,

⇒ 126 + 84 = 210

⇒ New average of 7 numbers = 210/7 = 30

∴ New average is 30
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