Are the numbers 12, 18, 20 and 30 in proportion, taken in that order?

Class 6Ratio and ProportionRatio and Proportion

Step-by-Step Solution

For 12 : 18 :: 20 : 30 the test is the cross product: extremes

12 \times 30 = 360

and means

18 \times 20 = 360

. They match, so the four numbers are in proportion. Adding the terms, or multiplying the first two against the last two, is not the proportion test.

Answer: A) Yes, because

12 \times 30 = 18 \times 20 = 360

If a :

b = c : d

, the four numbers are in proportion. The classic check: the **product of the extremes**

(a \times d)

equals the **product of the means**

(b \times c)

. Example: are 4 : 6 and 6 : 9 in proportion? Cross-multiply:

4 \times 9 = 36, 6 \times 6 = 36

. Equal → yes, in proportion.

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