Happy Island has 60 turtles. This means there are 10 more than 2 times as many turtles on Happy Island as on Lonely Island. How many turtles are there on Lonely Island? Think carefully first, then make a decision:
After subtracting 10 from the number of turtles on Happy Island, we get 60 - 10 = 50 turtles. Dividing this number by two, we find that the number of turtles on Lonely Island is 50 / 2 = 25 turtles. So, the answer is 25.