What would be the final temp of a mixture of 50gms of water at 20 degrees centigrade temp and 50gms of water at 40degrees centigrade temp

Answer 1

Use
T=(m1T1+m2T2)/(m1+m2)
=(50*20+50*40)/(50+50)
=30°C

Note: special case when the masses are equal, and the liquids are identical, the temperature is the mean of the two liquid temperatures.