Correct Answer - Option 3 : 8.75
Given
33x - y = 81
3x + y = 729
Formula/ Concept used
If am + n = ap then m + n = p
where m, n and p are real numbers.
Calculation
33x - y = 34
3x-y = 4 ......(1)
3x + y = (32)3
x + y = 6 ......(2)
on adding equation (1) and (2)
4x = 10
x = 2.5
put x= 5 in equation (2)
y = 6 - x
y = 6 - 2.5 = 3.5
∴ x × y = 2.5 × 3.5 = 8.75