The mean high temperature of the first four days of a week is 25°C whereas the mean of the last four days is 25.5°C. If the mean of the whole week is 25.2°C, then the temperature of the 4th day is-

Average temperature of first four days = 25°C
Total temperature of first four days = 25° × 4 = 100°C
Average temperature last four days = 25.5°C
Total temperature of four days = 25.5° × 4 = 102°C
Total temperature of whole week = 25.2° × 7 = 176.4°C
∴ Temperature of the 4th day
= 100° + 102° - 176.4°
= 25.6°C