Ella has more than 5 sweets and her friend Susie has three times as many.

Ella gives 5 sweets to Susie.

Susie gives Ella three times the amount of sweets that Ella had left after giving some of her sweets to Susie.

No matter how many sweets Ella has to start with (provided they are more than 5), Susie will always end up with the same amount of sweets!