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  1. If average of two numbers x and
    1
    (where x ≠ 0) is A, what will be the average of x3
    1
    ?
    xx3

    1. 4A3 - 2A
    2. 4A3 - 3A
    3. 4A3 - 4A
    4. 4A3 - A
Correct Option: B

According to the question ,

A = 1 +
1
x
2

⇒ x +
1
= 2A
x

On cubing both sides,
x +
1
3 = (2A)3 = 8A3
x

⇒ x3 +
1
+ 3x +
1
= 8A3
x3x

⇒ x3 +
1
+ 3 × 2A = 8A3
x3

⇒ x3 +
1
= 8A3 - 4A
x3

∴ Required average = x3 +
1
x3
2

Required average =
8A3 - 4A
= 4A3 - 2A
2



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