# If a single MBP has a 50% probability of being flawless and you purchase two of them, what is the

Discussion in 'MacBook Pro' started by Hieveryone, Mar 19, 2017.

1. Mar 19, 2017
Last edited: Mar 19, 2017

### Hieveryone macrumors 68030

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Apr 11, 2014
#1
combined probability both will be flawless, and the combined probability both will be flawed?

Let's say they each have a 50% chance of being flawed or flawless.

Sorry it's an odd question, but I was curious what the answer was. I'm arguing this with a friend right now.

2. ### smallcoffee macrumors 65816

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#2
.5*.5 = .25 assuming just a binary flawed or not, so the probability that one of the two would have a flaw would be 75%.

But the probabilities of a flawed MacBook Pro are much lower than that, and it's far more complicated than that as well. You'd have to take into account variable factors of failure rates/components, and look at different hardware configurations, etc....

3. ### Hieveryone thread starter macrumors 68030

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Apr 11, 2014
#3
THANK YOU!!!! I got it right but saw it wrong, meaning interpreted the numbers wrong. But at least the math I did and the method I did was right.

4. ### MacNut macrumors Core

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#4
Shocking. Although you never get anything wrong so why am I not surprised.

Joined:
Sep 6, 2002
#5

6. ### DeltaMac macrumors G3

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Jul 30, 2003
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Delaware
#6
And - your math actually is wrong.
Quantity doesn't change the probability on each unit.
With your original assertion that there's a 50% chance of a fault, then each one that you buy has that same 50% shot at greatness.
Buy 20, you still have 50% chance of faults on each one.
(Buying units in quantity won't lessen your chance of any individual unit having a fault.)

7. ### smallcoffee macrumors 65816

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#7
The OP asked about the probability for two of them, not each individually. The probability for any given combination will be 1/4.

Just like a coin, you have the following possibilities {T/T, T/F, F/T, F/F}. The probability of having one with a failure is therefore 3/4, or .75.

8. ### Hieveryone thread starter macrumors 68030

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Apr 11, 2014
#8
YES! The probability for 2 of them NOT individually. If you count the chance of any one being flawless or flawed, it's 50% no matter how many you buy I think!

9. ### chabig macrumors 601

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Sep 6, 2002
#9
Quoting from the thread title, "If a MBP has a 50% chance of being flawed or flawless, what are your chances of it being flawless..."

10. ### smallcoffee macrumors 65816

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#10
Read the rest of the post. Besides, OP has clearly confirmed what they were asking. What in the world is the controversy about?

11. ### DeltaMac macrumors G3

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Jul 30, 2003
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Delaware
#11
Yep
Probability is easiest to mis-interpret, particularly if you don't consider sets correctly, or miss that "sets" are not the key factor, and you get to remember that individual units can decide the result (not the set)

12. ### chabig macrumors 601

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Sep 6, 2002
#12
The OP should edit the title, as I said earlier.

13. ### Hieveryone thread starter macrumors 68030

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Apr 11, 2014
#13
Wait, what's wrong with the title?

14. ### chabig macrumors 601

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Sep 6, 2002
#14

The title should say, "If a single MBP has a 50% probability of being flawless and you purchase two of them, what is the combined probability that both will be flawless."

15. ### C DM macrumors Westmere

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Oct 17, 2011
#15
What's with the run on thread title that just cuts off?

16. ### Hieveryone thread starter macrumors 68030

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Apr 11, 2014
#16
I changed it up and added some as well!
--- Post Merged, Mar 19, 2017 ---
It doesnt' fit!

17. ### C DM macrumors Westmere

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Oct 17, 2011
#17
Well, it's a title, it's not supposed to be the whole post or some cut off first sentence of a post.

18. ### Hieveryone thread starter macrumors 68030

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Apr 11, 2014
#18
How could I ahve made it shorter?

19. ### C DM macrumors Westmere

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Oct 17, 2011
#19
Create a title for what the thread is about and ask the actual questions and provide details in the thread itself? Let's say something along the lines of "Probability of flawless MBPs" for the title perhaps.

20. ### leman macrumors G3

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Oct 14, 2008
#20
Don't people go to school anymore? I thought that basic combinatorics was a mandatory subject?

### Staff Member

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#21
Agreed, I think Macs still well made and the risk of getting a defect is rather low.

22. ### thesaint024 macrumors 65816

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suspension waiting room
#22
Haha. This probably came up in high school math somewhere, but I didn't actually get a class in probabilities until college. And even then, I don't think it was compulsory for everyone. But yeah, it's still a rather easy question for anyone who's placed a wager, even a little. Yes, the US school system is not very good, and it will likely get worse (speaking of my experience, not OP's).

23. ### smallcoffee macrumors 65816

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#23
Yeah. In general most computers are made pretty well. Especially now where we have reduce the number of moving components to at or near 0. There just isn't much there to be broken. With battery swaps possible, you could hang on to a new 2016 MacBook Pro for 5-8 years I think.

The main issue with windows pcs is the operating system, not the hardware.

24. ### Branflaakes macrumors 6502

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Aug 14, 2016
#24
Guys...seriously?

The probability of each unit being flawless, in OP's scenario, is 50%, irregardless of how many bought. However, the PROBABILITY of buying two and having BOTH of them being flawless is (1/2)(1/2) = 25%

25. ### MrGuder macrumors 68020

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Nov 30, 2012
#25
No offense but this is a classic click and bate thread title. It's thread titles like this that show people have too much free time and start making silly juvenile posts/threads. I see no benefit in this topic or way it can help others just silly banter.