I have $3$ lists of things. I want to choose things randomly from this lists.
But have percentage limitation on the lists. Like I can select only $60$% things from $1$st list, $30$% from $2$nd list & $10$% from $3$rd list.
I want to achieve this by a mathematical formula which can provide me a random selection for this lists in the provided percentages.
So lets say I am going to select $100$ things from this lists randomly. Then I must choose $60$ things from $1$st list, $30$ from $2$nd & $10$ from $3$rd list.
But the selection of the list must be random. I can not go straight away to select $60$ things from $1$st list then $30$ from $2$nd & so on.
As I am not that good in maths, can anyone please help me out so solve this problem.