Given:

The average temperature of 3 days - Monday, Tuesday and Wednesday is 60°C.

The average temperature of Tuesday and Wednesday is 52.5° C.

The temperature on Wednesday was twice the temperature on Tuesday.

Concepts used:

Average temperature = (Sum of temperature on all days)/(Number of days)

Calculation:

Sum of temperature on Monday, Tuesday and Wednesday = 60°C × 3 = 180°

Sum of temperature on Tuesday and Wednesday = 52.5°C × 2 = 105°C

The temperature on Monday = Sum of temperature on Monday, Tuesday and Wednesday – Sum of temperature on Tuesday and Wednesday  

⇒ Temperature on Monday = 180°C - 105°C = 75°C

Let the temperature on Wednesday and Tuesday be x°C and y°C respectively.

⇒ x = 2y      ----(1)

So, x + y = 105°C      ----(2)

Putting the value of x from eq (1) into eq (2),

⇒ 2y + y = 105°C

⇒ 3y = 105°C

⇒ y = 35°C

⇒ x = 2y = 2 × 35°C = 70°C

⇒ Sum of temperature on Monday and Wednesday = 75°C + 70°C = 145°C

∴ The sum of temperature on Monday and Wednesday is 145°C.