Mean of the observation is given by –

Total number of observations = 25

Mean of 25 observation = 27 (Given)

We get

⇒ Sum of 25 observations = 27 × 25 = 675

If each observation is decreased by 7, the Sum gets affected.

New Sum = 675 – (25 × 7) = 675 – 175 = 500

Thus, new mean = 20