When you take a bath, how many kilograms of hot water (49 degrees Celsius) must you mix with cold water (13 degrees Celsius) so the temperature of the bath is 36 degrees Celsius? The total mass of water (hot and cold) is 191 kg. Ignore any heat flow between water and it's external surroundings.
Total mass is 191:
m1+m2=191 mix of 49C and 13C water must five 36C water. Hence