The average temperature of first three days of the week is 23°C; the average temperature of next three days is 24°C and the average temperature of whole week is 23.5°C. The temperature on the last day of the week is:

23.5°C

ATQ,

 Sum of temp. of 1st 3 days = 69°C

 Sum of temp. of next 3 days = 72°C

 Sum of temp. of whole week = 164.5°C

 Temp. on last day of the week = 164.5 - 69 - 72= 23.5°C