# 2Coins probability of Heads-tails in 40 tosses? HELP!

1. Mar 25, 2005

### aisha

2 coins are tossed at the same time There are 3 colums in a chart

3)Tails-Tails

the coins were tossed 40 times simultaneously.

What was the probability that heads-tails (or tails-heads) would appear? Show calculations.

(HINT: The probability of these two combinations must be added together because they were recorded together.)

Im thinking its 2/4 but not sure, and dont know what to show as calculations.

2. Mar 25, 2005

### TsunamiJoe

but im not so great with it either, but wouldnt it be 1/3 chance for all?

3. Mar 25, 2005

### aisha

4. Mar 26, 2005

### BobG

Yes, you're correct.

You have a 50% chance of coin 1 coming up heads. If coin 1 comes up heads, you have a 50% chance of coin 2 coming up heads. .5 * .5 gives you a 25% chance of both coins coming up heads.

If you do the same for each combination, you wind up with a 25% chance of each combination coming up. Since the coins are tossed simultaneously, you don't know if you have heads-tails or tails-heads. So you add the probabilities for both combinations together.

5. Mar 26, 2005

### Staff: Mentor

Unless, of course, you have two different coins (say a quarter and a loonie) and it matters which one is which. Then you would consider loonie-heads and quarter-tails as a different outcome from loonie-tails and quarter-heads, each with 25% probability.

6. Mar 26, 2005

### aisha

can u show me what the calculation would look like BOB? I understand what your saying but not 100% sure.

7. Mar 26, 2005

### GCT

If this pertains to statistics, you'll need to employ proper formulas and concepts to solve this equation, it may NOT be 1/2.

8. Mar 26, 2005

### aisha

no this is not physics it was just a Bio lab using a little bit of probability to help understand mendel and the pea plant .