Answer:
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
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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.
