Given,
Specific heat of water SW=4.2 kJ/kg K
Mass of cold, water,MC=0.3kg
Mass of hot, water, MH=0.2kg
If final temperature is Tf
Heat Loos = heat gain
MHSW(80−Tf)=MCSW(Tf−10)
Tf=MHSW×80+MCSW×10MHSW+MCSW
Tf=0.2×4.2×80+0.3×4.2×100.2×4.2+0.3×4.2
Tf=38oC
Final temperature of mixture is 38oC