A student carries out a titration three times and obtains the following volumes: $3.0 \pm 0.1{\text{ c}}{{\text{m}}^3}$, $3.2 \pm 0.1{\text{ c}}{{\text{m}}^3}$ and $3.2 \pm 0.1{\text{ c}}{{\text{m}}^3}$. What is the average volume?

A.     $3.1 \pm 0.1{\text{ c}}{{\text{m}}^3}$

B.     $3.13 \pm 0.1{\text{ c}}{{\text{m}}^3}$

C.     $3.1 \pm 0.3{\text{ c}}{{\text{m}}^3}$

D.     $3.13 \pm 0.3{\text{ c}}{{\text{m}}^3}$

A

This was the second most difficult question of the paper. Most candidates answered C or D, not realizing that, if correct, repeats would then increase the uncertainty.