If each observation of a data set is multiplied by 3, the mean of the new data is ____ times the original mean.

**Setup**: data given as class intervals with frequencies. Compute class marks $x$ᵢ.

**Formula**: **$x$̄ = Σ$(f$ᵢ$x$ᵢ) / Σ$f$ᵢ**

Multiply each class mark by its frequency, sum, divide by total frequency.

**Example**:
| Class | $f|x$ (mark) | $fx$ |
|---|---|---|---|
| 0–10 | 5 | 5 | 25 |
| 10–20 | 8 | 15 | 120 |
| 20–30 | 7 | 25 | 175 |

Σ$f=20$, Σ$fx=320$. Mean = 320/20 = 16.

**When to use**: small class marks; arithmetic stays manageable.