math questions, assistance please

[Gordon9721]

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ok, questions with answers, but i need reasons why these are the answers:

why is x = (2/y)b parallel to the y-axis?
y should have a degree notation on it....

A fly sits at the edge of a 12 inch diameter phonograph record that is playing at 33.3 revolutions/minute. Approximately how fast, in feet per minute, is the fly moving?
answer: 100
why?

variance of numbers?
what are the arithmetic mean and the variance of the set of numbers 2, 8, 10, 16?

thanks in advance

 

[Gordon9721]

sqrt=square root

sqrt15 x sqrt3 / sqrt10 = ?

answer is 3sqrt2 / 2

but i keep getting 3 / sqrt 2

ahhhhhhhhhhhh

 

[TKO]

Not sure about the parallel question but the others I know.

2. The diameter of the record is 12 inches so the radius in 6 inches. The circumference of the record is the 2(pi)r = 12inches(pi) = 1 foot(pi). Since the fly is sitting on the edge of the record, it will move the same distance as the circumference during one full revolution of the record. So its [1 (pi) feet / revolution] x [33.3 revolutions/minute] = about 3 x 33.3 = 100.

3. Variance is the summation of square of the difference of each number from the average.

4. Your answer is equivalent to the correct answer, you just have to multiply the numerator and denomenator of your answer by sqroot2 to get thier choice.

 

[dentist268]

Why did you multiply by 3?


got it!....It's because of pi