Energy Used during Bike race?

Question

In a hot day’s race, a bicyclist consumes 8 liters of water over the span of four hours.
Let us assume that 80% of his energy goes into evaporating this water as sweat. (This is
not a bad approximation, because the mechanical efficiency of a bicycle rider is only
about 20%, with the rest of the energy consumed going into heat.) How much total
energy, in kcal, did the rider use during the race?

Answer 1

odu83 has it half right. He forgot to take into account that only 80% of the total energy is being evaporated. So you take Q=8kg*2260 kJ/kg
Q=18080J
18080/80%=Qtotal/100%
so
Qtotal=18080*100/80=22600J

22600J*(0.239005736 cal/1J)*(.001kcal/1 cal)=5.4kcal

Answer 2

the latent heat of evaporation is 2260 kJ/kg
1 liter is 1 kg and
1 J=0.239005736 cal

4,321 kcal

j