Answer: Ratios form a proportion if they are equal when cross-multiplied.
1/4 and 3/12
Cross-multiply these ratios to compare them: 1/4 * 12 = 3, 3/12 * 4 = 3.
So they are equal and form a proportion.
54/10; 81/15
Cross-multiply these ratios to compare them: 54/10 * 15 = 81, 81/15 * 10 = 54.
So they are equal and form a proportion.
18/24; 15/20
Cross-multiply these ratios to compare them: 18/24 * 20 = 15, 15/20 * 24 = 18.
So they are equal and form a proportion.
Hence, all the ratios mentioned above form a proportion.
Explanation: