self Maths Puzzle

There are 100 light switches on the wall, all turned off. A hundred toddlers come by. The first toddler flips every
switch. Then the second toddler flips just switches 2, 4, 6, 8, ... etc. Then the third toddler flips switches 3, 6,
9, 12, ... etc. This pattern continues until finally the 100th toddler flips just switch number 100. How may lights
are turned on at the end?

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self Other Question
At a bar, there is a bucket containing ice, some of which has melted. A bartender gets an ice cube weighing 20 grams from the ice bucket and puts it into an insulated cup containing 100 grams of water at 20 degrees Celsius. Will the ice cube melt completely? What will be the final temperature of the water in the cup? If 2505 / 0.5 = 5010 then 25.05 / 0.5 = ?