Question

what would be the final temperature of a mixture of 50g of water at 20°c temperature and 50g of water at 40°C temperature? (ASI)

Answer 1

Let the final temperature be T.
Heat lost by water at 40°C is gained by water at 20°C. Thus

$m_1s \Delta T_1=m_2s \Delta T_2\\ \\ 50 \times s \times (40-T)= 50 \times s \times (T-20)\\ \\40-T=T-20\\ \\T+T=40+20\\ \\2T=60\\ \\T= \frac{60}{2}=30^0C$

Final Temperature is 30°C

Answer 2

by using the method of mixture formula,
final temperature T = M1×T1+M2×T2/ M1+M2
                             = 50×20 + 50×40/50+50
                             = 100+200/100
                             = 300/100
                             = 30 degrees c 
therefore final temperature T = 30 degrees C