If a/b >c/d are both positive fractions, do we have ad > bc? If so, why?

 NO. if a/b > c/d,   a/d is not greater than b/c

Step-by-step explanation:   The the larger the number in the denominator, the smaller its value as it is represents fractional value, not a whole number. So when a "small" numerator is moved to a denominator, it increases in size, and the large number in the numerator moved to a denominator decreases in size.  

Moving the denominator from a smaller fraction to the left side will diminish the value of the new fraction.

3/4 > 1/2  but 3/2 < 4/1

7/8 > 5/6 but  7/6 < 8/5

1/2 > 1/4  but   1/4 < 2/1  

the arc length is found by finding the circumference of the full circle (2xpixradius) and then dividing by 4 to find just one quarter of the circle (90 degrees).

3/20

step-by-step explanation:

well, there are 20 outcomes, and 3 of them you want. so, 3/20