If a : b = 3 : 4 and b : c = 5 : 9, then a : b : c is

To find the ratio a : b : c, we need to combine the given ratios.

Step 1: Write down the given ratios. a : b = 3 : 4 b : c = 5 : 9

Step 2: Notice that the term 'b' is common in both ratios. We need to make the 'b' terms in both ratios equal so we can combine them.

Step 3: To make the 'b' terms equal, we can cross-multiply the ratios. Multiply the first ratio by 5 (the 'b' term in the second ratio) and the second ratio by 4 (the 'b' term in the first ratio).

(3 : 4) * 5 = 15 : 20 (5 : 9) * 4 = 20 : 36

Step 4: Now that the 'b' terms are equal (20), we can combine the ratios to get a : b : c.

a : b : c = 15 : 20 : 36

So, the ratio a : b : c is 15 : 20 : 36.