The average height of 30 students is 150 cm. It was detected later that one value of 165 cm was wrongly copied as 135 cm for the computation of mean. Find the correct mean.

Mean = $\dfrac{\text{Sum of observations}}{\text{No. of observations}}$

∴ Sum of observations = Mean × No. of observations
⇒ Sum of observations = 150 × 30 = 4500.

Since, one value of 165 cm was wrongly copied as 135 cm,

∴ Correct sum of observations = 4500 - 135 + 165 = 4530.

Correct mean = $\dfrac{\text{Sum of observations}}{\text{No. of observations}} = \dfrac{4530}{30}$ = 151.

Hence, the correct mean is 151 cm.