arrow
arrow
arrow
If 3x-2y=10 and xy=11, the value of 27x3−8y327x^3-8y^327x3−8y3​ is
Question

If 3x-2y=10 and xy=11, the value of 27x38y327x^3-8y^3​ is

A.

2980

B.

2569

C.

3336

D.

3170

Correct option is A

Given:
3x - 2y = 10 and xy=11

Formula used:
(ab)3=a3b33ab(ab)(a - b)^3 = a^3 - b^3 - 3ab(a - b) \\​​
Solution: 
3x2y=10Taking a cube on both sides of the above equation:(3x2y)3=10327x38y33(3x)(2y)(3x2y)=100027x38y318(xy)(3x2y)=1000Substitute: 3x2y=10, xy=1127x38y3181110=100027x38y31980=100027x38y3=1980+100027x38y3=2980Hence, the value of 27x38y3 is 2980.3x - 2y = 10 \\\text{Taking a cube on both sides of the above equation:} \\(3x - 2y)^3 = 10^3 \\27x^3 - 8y^3 - 3(3x)(2y)(3x - 2y) = 1000 \\27x^3 - 8y^3 - 18(xy)(3x - 2y) = 1000 \\\text{Substitute: } 3x - 2y = 10, \, xy = 11 \\27x^3 - 8y^3 - 18 \cdot 11 \cdot 10 = 1000 \\27x^3 - 8y^3 - 1980 = 1000 \\27x^3 - 8y^3 = 1980 + 1000 \\27x^3 - 8y^3 = 2980 \\\textbf{Hence, the value of } 27x^3 - 8y^3 \text{ is } 2980.​​

Free Tests

Free
Must Attempt

CBT-1 Full Mock Test 1

languageIcon English
  • pdpQsnIcon100 Questions
  • pdpsheetsIcon100 Marks
  • timerIcon90 Mins
languageIcon English
Free
Must Attempt

RRB NTPC Graduate Level PYP (Held on 5 Jun 2025 S1)

languageIcon English
  • pdpQsnIcon100 Questions
  • pdpsheetsIcon100 Marks
  • timerIcon90 Mins
languageIcon English
Free
Must Attempt

CBT-1 General Awareness Section Test 1

languageIcon English
  • pdpQsnIcon40 Questions
  • pdpsheetsIcon30 Marks
  • timerIcon25 Mins
languageIcon English
TEST PRIME

Access ‘RRB Group D’ Mock Tests with

  • 60000+ Mocks and Previous Year Papers
  • Unlimited Re-Attempts
  • Personalised Report Card
  • 500% Refund on Final Selection
  • Largest Community
1 month
Monthly Saver
students-icon
354k+ students have already unlocked exclusive benefits with Test Prime!
Our Plans
Monthsup-arrow