Finally, here is the solution to this enigma... I hope you enjoyed it, and that you'll enjoy the one of this week...
If we note Girl-i the age of the girl "i" (without any link between "i" and the order of the girls), we have :
Girl-1*Girl-2*Girl-3=36, there are different possibilities :
36*1*1
18*2*1
9*2*2
9*4*1
6*3*2
6*6*1
12*3*1
4*3*3
Furthermore, we've got Girl-1+Girl-2+Girl-3= Number.
36+1+1=38
18+2+1=21
9+2+2=13
9+4+1=14
6+3+2=11
6+6+1=13
12+3+1=16
4+3+3=10
The person knows this number but can't find the answer the same... There are only two possibilities that have the same sum : (9 ; 2 ; 2) and (6 ; 6 ; 1).
Finally, when the father says the oldest one has got blue eyes, it means that it can't be the case in which the girls are 6 years old, 6 years old and 1 year old because two of them would have the same age and there wouldn't be an oldest one. So the answer can only be 9 years, 2 years and 2 years.
Congratulations to Thibault, Florian, Charlotte and Irene who managed to find this answer. I thought it would take more time, but that's not a problem.
