The mean high temperature of the first four days of a week is $$25^\circ c$$ whereas the mean of the last four days is $$25.5^\circ c$$ then the temperature of the $$4^{th}$$ day is:

A week has 7 days.

given that mean temperature of first 4 days is 25

i.e; sum of total temperatures of first 4 days=4*25=100.........(1)

Also given that mean temperature of last 4 days=25.5

i.e; sum of total temperatures of last four days=25.5*4=102..........(2)

so, Total temperature of the week = 25.2*7 = 176.4..........(3)

Adding (1) and (2) , i.e; 100 + 102 = 202.............(4)

Subtracting (3) from (4), we get , the get the 4^th day temperature

i.e; 202-176.4 = 25.6