- 125
- 120
- 110
- 115

Option 3 : 110

**GIVEN: **

(a + 1/4a) = 5/2

**FORMULA USED: **

(a + b)^{3} = a^{3} + b^{3} + 3ab (a + b)

**CALCULATION: **

(a + 1/4a) = 5/2

⇒ (2a + 1/2a) = 5

Taking cube both sides:

⇒ 8a^{3} + 1/8a^{3 }+ 3 × 2a × 1/2a × (2a + 1/2a) = 125

⇒ 8a^{3} + 1/8a^{3 }+ 15 = 125

⇒ 8a^{3} + 1/8a^{3 }= 110

∴ The value of (8a3 + 1/8a3) is 110.

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