Correct Answer - Option 4 : 39°C

**Given:**

The average temperature on Monday, Tuesday and Wednesday = 40°C

Temperature of Tuesday, Wednesday and Thursday = 41°C

Temperature of Thursday = 42°C

**Formula used: **

Mean = Sum of no. observation/No. of observation

**Calculation:**

Average temperature for Monday, Tuesday and Wednesday = 40°C

Total temperature = 3 × 40 = 120°C

Average temperature for Tuesday, Wednesday and Thursday = 41°C

Total temperature = 41 × 3 = 123°C

Temperature on Thursday = 42°C

⇒ (Tuesday + Wednesday + Thursday) - (Monday + Tuesday + Wednesday) = 123° - 120°

Thursday - Monday = 3°

Monday = 42° - 3° = 39°C

**∴ The temperature on Monday is 39°C.**