Which ratios form a proportion? use cross products to test each pair.
a. 15/40, 35/90
b. 18/22, 45/55
c. 15/55, 33/121
d. 17/31, 32/45

B. 18/22, 45/55

C. 15/55, 33/121

Step-by-step explanation:

Cross products are ...

A. 15×90 = 1350 ≠ 1400 = 40×35 . . . . not a proportion

B. 18×55 = 990 = 22×45 . . . . ratios are a proportion

C. 15×121 = 1815 = 55×33 . . . . ratios are a proportion

D. 17×45 = 765 ≠ 992 = 31×32 . . . . not a proportion

Comment on the solution

When looking at cross products, it can work well to look at the factors of the numbers involved:

... 18×55 = 2·9·5·11 . . . . . . 22·45 = 2·11·9·5 . . . . the same list of factors

You don't actually need to multiply it out to see that the products will be equal.

In pair D, you may recognize that 31 is a prime number, so the other ratio will only be proportional if the denominator is a multiple of 31, which it is not.

A line of best fit can only be drawn if there is strong positive or negative correlation. The line of best fit does not have to go through the origin. The line of best fit shows the trend, but it is only approximate and any readings taken from it will be estimations.

Step-by-step explanation: