Jaylan : Water/Juice=(3/4)/(1/5)=15/4
Wanchen : Water/Juice=(2/3)/(1/6)=4/1 or 16/4
Wanchen has a weaker lime flavor because there is more water in her mixture than Jaylan's limeade. Both have the same amount of lime juice (assuming ratio), and Wanchen has more water, making Wanchen have the limeade that has the weaker lime flavor.