Question:hard

If the mean deviation of the data \[ 1,\ 1+d,\ 1+2d,\ \ldots,\ 1+100d \quad (d\gt 0) \] from their mean is \(255\), then \(d\) is equal to

Show Hint

For an arithmetic progression with an odd number of terms, deviations from the mean occur symmetrically around zero. Use symmetry to simplify mean deviation calculations.
Updated On: Jun 22, 2026
  • \(10.1\)
  • \(10.2\)
  • \(10.3\)
  • \(10.4\)
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Write the data set.
The data is $1, 1+d, 1+2d, \ldots, 1+100d$, which is an AP with 101 terms, first term $a_0=1$ and common difference $d > 0$.
Step 2: Find the mean.
Mean $\bar{x} = \frac{\text{Sum}}{101}$. Sum $= 101 \cdot 1 + d(0+1+2+\cdots+100) = 101 + d \cdot \frac{100 \cdot 101}{2} = 101 + 5050d$. So $\bar{x} = 1 + 50d$.
Step 3: Compute deviations from mean.
$|x_k - \bar{x}| = |(1+kd) - (1+50d)| = |k-50|d$ for $k = 0, 1, 2, \ldots, 100$.
Step 4: Compute the mean deviation.
Mean deviation $= \frac{1}{101} \sum_{k=0}^{100} |k-50|d = \frac{d}{101} \sum_{k=0}^{100} |k-50|$.
$\sum_{k=0}^{100} |k-50| = 2(1+2+\cdots+50) = 2 \cdot \frac{50 \cdot 51}{2} = 2550$.
Step 5: Set the mean deviation equal to 255.
$\frac{d \cdot 2550}{101} = 255$. So $d = \frac{255 \times 101}{2550} = \frac{101}{10} = 10.1$.
Step 6: Match with options.
$d = 10.1$ is option (1).
\[ \boxed{d = 10.1} \]
Was this answer helpful?
0