I've implemented the function:

 function coinFlip() {
      return(Math.floor(Math.random()*2) === 0) ? 'Heads' : 'Tails';
 }

And it's all working fine (I already tested it).

My problem is, how do I make this function so that the probability of getting 'Heads' is 30% while the probability of getting 'Tails' is 70%?

Thanks in advance

I've implemented the function:

 function coinFlip() {
      return(Math.floor(Math.random()*2) === 0) ? 'Heads' : 'Tails';
 }

And it's all working fine (I already tested it).

My problem is, how do I make this function so that the probability of getting 'Heads' is 30% while the probability of getting 'Tails' is 70%?

Thanks in advance

• javascript
• probability
• coin-flipping

Share Improve this question Follow asked Jul 4, 2016 at 0:17 5120bee5120bee 70922 gold badges1616 silver badges3838 bronze badges 5

• 1 Pick a random number between 0 and 1. If the number is <0.3 it's Heads. Else, it's Tails... – Maria Ines Parnisari Commented Jul 4, 2016 at 0:19
• Okay, but suppose that I do 10 coin flips. I want to print out the results and by logic, 3 of those will be heads and 7 will be tails. How do I implement that? – 5120bee Commented Jul 4, 2016 at 0:21
• it is not a sure thing that 3 of those will be heads and 7 of those will be tails. Over many many repeated experiments, the average will be 3 heads and 7 will tails – derp Commented Jul 4, 2016 at 0:22
• "3 of those will be heads"? Um, no. 3 of those will most likely be heads. Use an array – Maria Ines Parnisari Commented Jul 4, 2016 at 0:22
• I already put them in an array. Like I said, I tested everything out and all is working in order. I just wanted a possible solution for how to solve a specific percentage problem. EDIT: I have my entire code working, I just didn't put it on here since my only problem is getting the correct percentage for the heads/tails result. – 5120bee Commented Jul 4, 2016 at 0:24

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2 Answers 2

Sorted by: Reset to default 6

function coinFlip() {
      return(Math.random() < 0.3) ? 'Heads' : 'Tails';
 }

If one of three toss coin is head it doesn't mean that in 10 toss, there will be 3 heads.. Here is your code with 500 toss (just change the number)

    function coinFlip() {
          return(Math.random() < 0.3) ? 'Heads' : 'Tails'; //ofc 0.3 is 30% (3/10)
    }

 var howManyTimes=500;
 var countHeads=0; 
 for (var i=0; i<howManyTimes;i++){
     if (coinFlip()==='Heads'){
       countHeads++;
     }
 }
 alert("Heads appear "+(countHeads/howManyTimes)*100+"% of the time");

"how to solve a specific percentage problem"

You can't, this is how probability works