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 :

According to the question,
⇒ Total temperature of first four days
Mon + Tue + Wed + Thu
= 25 × 4 = 100°C.....(i)
⇒ Total temperature of last four days
Thu + Fri + Sat + Sun
= 25.5 × 4 = 102°C .....(ii)
⇒ Total temperature of week
= 25.2 × 7 = 176.4°C .....(iii)
After adding equation (i) + (ii)
Mon + Tue + Wed + 2 × Thu + Fri + Sat + Sun
= 100° + 102° = 202°C.....(iv)
After subtracting equation (iv) - (iii)
= 202° - 176.4° = 25.6° C
⇒ Temperature of 4th day = 25.6° C