Given,
the final temperature of mixture = T °C
for hot water,
mass m1 = 10 kg
temp t1 = 90°C
specific heat capacity of water = 4200 J/kg °C
Also for cold water
mass m2 = 20 kg
t2 = 10°C
specific heat capacity s = 4200 J/kg°C
By the formula ,
\(T\;=\;\frac{m_1s_1t_1+\;m_{2\;}s_{2\;}t_2}{m_1s_1+m_2s_2}\)
T = 36.66 °C