The values are 4, 6, 6, 7, 12. Find the mean, the median and the mode.

Step 1. The averages. Total $= 35$, so the mean is $\dfrac{35}{5} = 7$. The middle value is $6$, and $6$ appears twice, so the median and the mode are both $6$.

Step 2. Add 10. The values become $14, 16, 16, 17, 22$. The mean is $17$, the median $16$ and the mode $16$.

Step 3. What we notice. All three averages went up by exactly $10$. If every value were doubled, all three would double: $14$, $12$ and $12$.