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Out of five numbers, the average of first four numbers is 30 and that of last 4 numbers is 28, whereas fifth number is 10. Find the first number.

Out of five numbers, the average of first four numbers is 30 and that of last 4 numbers is 28, whereas fifth number is 10. Find the first number. Correct Answer 18

Given:

Average of first four numbers = 30

Average of last four numbers = 28

Fifth number = 10

Formula used:

Average = (sum of all observation)/Number of observation

Calculation:

Sum of first 4 numbers(I, II, III and IV) = 30 × 4

⇒ 120

Sum of last 4 numbers (II, III, IV and V) = 28 × 4

⇒ (II + III + IV + 10) = 112

⇒ (II + III + IV) = 102

⇒ (I + II + III + IV) = 120

⇒ I + 102 = 120

⇒ I = 120 - 102

⇒ I = 18

∴ First number is 18.

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