Answer: 3.712 hours or more
Step-by-step explanation:
Let X be the random variable that denotes the time required to complete a product.
X is normally distributed.

Let x be the times it takes to complete a random unit in order to be in the top 10% (right tail) of the time distribution.
Then, 
![P(z>\dfrac{x-3.2}{\sigma})=0.10\ \ \ [z=\dfrac{x-\mu}{\sigma}]](https://tex.z-dn.net/?f=P%28z%3E%5Cdfrac%7Bx-3.2%7D%7B%5Csigma%7D%29%3D0.10%5C%20%5C%20%5C%20%5Bz%3D%5Cdfrac%7Bx-%5Cmu%7D%7B%5Csigma%7D%5D)
As,
[By z-table]
Then,

So, it will take 3.712 hours or more to complete a random unit in order to be in the top 10% (right tail) of the time distribution.
So the formula is
7*(1/3+1/5) = x
First find the common denominator of the fractions. In this case the common denominator of 3 and 5 is 15 so we must convert them to 15ths. To do that we divide 15 by the denominator and take that answer and multiply the numerator by it.
So for 1/3 we take 15/3(denominator) = 5 and multiply the numerator (1) by it
5 * 1 = 5 so 1/3 converts to 5/15
Do the same for 1/5 we take 15/5 = 3 and multiply the numerator (4) by it
3*4 = 12 so 4/5 converts to 12/15
Now we add 5/15 and 12/15 = 17/15 so we have our formula now to
7*17/15
We make seven a fraction 7/1 and multiply across 7*17 = 119 and 15 * 1 = 15
We have 119/15 which when we divide and get 7 14/15 as your answer
I hate math its so hard for no reason
Here are the pairing:
The first tile should be paired with 4th property
The second tile should be paired with the 1st property
The third tile should be paired with the 3rd property
The fourth tile should be paired with the 2nd property