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

#### Hieveryone

##### macrumors 603
Original poster
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.

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#### smallcoffee

##### macrumors 68000
you bought 2 of them? 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.
.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....

Hieveryone

#### Hieveryone

##### macrumors 603
Original poster
.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%.
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.

#### MacNut

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

#### DeltaMac

##### macrumors G4
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.)

#### smallcoffee

##### macrumors 68000
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.)
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.

#### Hieveryone

##### macrumors 603
Original poster
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.
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!

#### chabig

##### macrumors 604
The OP asked about the probability for two of them, not each individually.
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..."

#### smallcoffee

##### macrumors 68000
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..."
Read the rest of the post. Besides, OP has clearly confirmed what they were asking. What in the world is the controversy about?

#### DeltaMac

##### macrumors G4
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)

#### chabig

##### macrumors 604
Read the rest of the post. Besides, OP has clearly confirmed what they were asking. What in the world is the controversy about?
The OP should edit the title, as I said earlier.

#### Hieveryone

##### macrumors 603
Original poster
The OP should edit the title, as I said earlier.
Wait, what's wrong with the title?

#### chabig

##### macrumors 604
Wait, what's wrong with the title?

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."

#### C DM

##### macrumors Sandy Bridge
you bought 2 of them? 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.
What's with the run on thread title that just cuts off?

#### Hieveryone

##### macrumors 603
Original poster

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."
I changed it up and added some as well!
[doublepost=1489985098][/doublepost]
What's with the run on thread title that just cuts off?
It doesnt' fit!

#### C DM

##### macrumors Sandy Bridge
I changed it up and added some as well!
[doublepost=1489985098][/doublepost]

It doesnt' fit!
Well, it's a title, it's not supposed to be the whole post or some cut off first sentence of a post.

DeltaMac

#### Hieveryone

##### macrumors 603
Original poster
Well, it's a title, it's not supposed to be the whole post or some cut off first sentence of a post.
How could I ahve made it shorter?

#### C DM

##### macrumors Sandy Bridge
How could I ahve made it shorter?
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.

#### leman

##### macrumors G4
Don't people go to school anymore? I thought that basic combinatorics was a mandatory subject?

DeltaMac

#### maflynn

##### Moderator
Staff member
But the probabilities of a flawed MacBook Pro are much lower than that
Agreed, I think Macs still well made and the risk of getting a defect is rather low.

#### thesaint024

##### macrumors 65816
Don't people go to school anymore? I thought that basic combinatorics was a mandatory subject?
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).

#### smallcoffee

##### macrumors 68000
Agreed, I think Macs still well made and the risk of getting a defect is rather low.
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.

#### Branflaakes

##### macrumors 6502
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%

#### MrGuder

##### macrumors 68030
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.

HenryDJP
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