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For the proportion 9 : 4 :: 45 : 20, which statement is correct?

Class 6Ratio and ProportionRatio and Proportion
  • AThe extremes are 4 and 45, and
  • BThe extremes are 9 and 20, and
  • CThe means are 9 and 20, and
  • DThe extremes are 9 and 45, and

Step-by-Step Solution

In a : b :: c : d the FIRST and LAST terms are the extremes, so here they are 9 and 20, while the middle terms 4 and 45 are the means. Both products come to 180, confirming the proportion. Calling 4 and 45 the extremes, or pairing 9 with 45, mixes up which terms sit on the outside.
Answer: B) The extremes are 9 and 20, and

Key idea: Proportion: when two ratios are equal

If a : , the four numbers are in proportion. The classic check: the **product of the extremes** equals the **product of the means** . Example: are 4 : 6 and 6 : 9 in proportion? Cross-multiply: . Equal → yes, in proportion.

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