Given: Standard Deviation, σ = 3.5
and Numbers are 2, 3, 2x, 11
We know that,
=> 12.25 = 1/16[16 + 8x + x2 + 4 + 4x + x2 + 64 - 48x + 9x2 + 196 - 28x + x2]
⇒ 12.25 × 16 = 280 – 64x + 12x2
⇒ 196 = 280 – 64x + 12x2
⇒ 12x2 – 64x + 280 – 196 = 0
⇒ 12x2 – 64x + 84 = 0
⇒ 3x2 – 16x + 21 = 0
⇒ 3x2 – 9x – 7x + 21 = 0
⇒ 3x(x – 3) – 7(x – 3) = 0
⇒ (3x – 7)(x – 3) = 0
Putting both the factors equal to 0, we get
3x – 7 = 0 and x – 3 = 0
⇒ 3x = 7 and x = 3
⇒ x = 7/3
Hence, the possible value of x are 7/3 and 3