A worker takes a random sample of 320 bolts and finds that 30 of them are either too long or too short, thus making them unusable. Estimate the number of unusable bolts in a production of 14,000 bolts.
1,313 bolts
1,400 bolts
1,300 bolts
1,320 bolts

- anonymous

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- anonymous

@JoannaBlackwelder

- JoannaBlackwelder

Can you find the probability of unusability using the 320 bolts with 30 of them unusable?

- anonymous

320 * 30?

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## More answers

- JoannaBlackwelder

No, it's the same formula as last time.

- JoannaBlackwelder

(number of unusable/total number)*100

- anonymous

@JoannaBlackwelder Well 30 were unusuable it said and the total number was 14,000, so it's 30 / 14,00 * 100?

- JoannaBlackwelder

We don't know how many are unusable when we have 14,000 total. That is what we are looking for. But we have both numbers when the total is 320 and the number unusable is 30.

- anonymous

Ok, so then it would be 30/320 right?

- JoannaBlackwelder

Right, *100 :-)

- anonymous

And then that is 0.09 and I would times that by 100 ?

- JoannaBlackwelder

Yep

- anonymous

And that's 9.37

- JoannaBlackwelder

Yep, I get 9.375 to be precise. :-)

- anonymous

Lol, right, so then...is there another step? To get it to be one of the answers?

- JoannaBlackwelder

Then we can use that value in the same formula, but when the total is 14,000

- JoannaBlackwelder

So, 9.375=(number unusable/14,000)*100

- JoannaBlackwelder

See how I wrote that formula?

- anonymous

Lol, not really...I got 0.066

- JoannaBlackwelder

It is probability = (number unusable/total number)*100

- JoannaBlackwelder

How did you get .066?

- anonymous

I did 9.375 / 14000 * 100

- JoannaBlackwelder

No, the 9.375 is the probability, not the number of unusable.

- JoannaBlackwelder

|dw:1432918347029:dw|
Any ideas how to solve?

- anonymous

Oh, okay, so...30 is still the number of unsuable then I divide that by 14000 and times it by 100?

- JoannaBlackwelder

No, the number unusable is what we are solving for in the equation I wrote above.

- JoannaBlackwelder

No, the 14000 is in the denominator and 100 is in the numerator, so we don't multiply those.

- JoannaBlackwelder

|dw:1432918612846:dw|

- anonymous

Oh so 100 divided by 14000 which is 0.007?

- JoannaBlackwelder

To clear the fraction, we can multiply both sides by 14000|dw:1432918686742:dw|

- JoannaBlackwelder

Yeah, we could do it that way too. :-)

- JoannaBlackwelder

9.375=0.00714unusable

- JoannaBlackwelder

Can you finish solving for unusable?

- anonymous

Yeah, so rounding it up it would be 1, 313? unusable Right?

- JoannaBlackwelder

Yep :-D

- anonymous

@JoannaBlackwelder Thank you kindly for your help, and also for being so patient, lol as you can see I'm really not the best at math. XP :)

- JoannaBlackwelder

No worries. It takes practice. :-) Happy studies!

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