Final answer:
After simplifying the second ratio 20:18 by dividing both numbers by 2, we get 10:9, which confirms that the ratios 10:9 and 20:18 are equivalent.
Step-by-step explanation:
To determine if the ratios 10:9 and 20:18 are equivalent, we can simplify the second ratio. Dividing both parts of the ratio 20:18 by the common factor of 2 gives us 10:9, which is exactly the same as the first ratio. Another method is to calculate the value of each ratio by dividing the first number by the second. For both ratios, 10 ÷ 9 and 20 ÷ 18, the result is approximately 1.111. Since both ratios simplify to the same numbers and their decimal values are equal, they are indeed equivalent.