No it does NOT make sense to state density in kilograms per square meter. Density has to be stated in terms of mass per unit of volume and NOT per unit of area.
Answer:
Step-by-step explanation:
For the random variable 
we define the possible values for this variable on this case ![[1,2,3,4,5]](https://tex.z-dn.net/?f=%20%5B1%2C2%2C3%2C4%2C5%5D)
. We know that we have 2 defective transistors so then we have 5C2 (where C means combinatory) ways to select or permute the transistors in order to detect the first defective:
We want the first detective transistor on the ath place, so then the first a-1 places are non defective transistors, so then we can define the probability for the random variable 
like this:
For the distribution of 
we need to take in count that we are finding a conditional distribution. given 
, for this case we see that ![N_2 \in [1,2,...,5-a]](https://tex.z-dn.net/?f=%20N_2%20%5Cin%20%5B1%2C2%2C...%2C5-a%5D)
, so then exist 
ways to reorder the remaining transistors. And if we want b additional steps to obtain a second defective transistor we have the following probability defined:
And if we want to find the joint probability we just need to do this:
And if we multiply the probabilities founded we got:
ANSWER
EXPLANATION
The given expression is;
We factor to obtain;
Multiply by the reciprocal of the second fraction
Cancel out common factors to get,
Calculate the volume of sand, the cone will be completely filled and the cylinder will have sand up to the 30 mm level.
Volume of sand will = the volume of the cone:
= 1/3 * pi * (6 mm)^2 * 15
= 1/3 * pi * 36 * 15 =180 pi cubic mm
the cylinder will have a volume of sand equal to:
= pi * (6 mm)^2 * 30 mm
= pi * 36 sq mm * 30 mm
= 1080 pi cubic mm
The total sand is the sum:
= 1080 pi cubic mm +180 pi cubic mm
= 1260 pi cubic mm.
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