1. Find the total of the ratio (2 + 3 + 5 = 10) 2. Work out what you do to 10 to get 30 (multiply by 3) 3. Multiply the blue ratio by three (3 x 3 = 9)
Check:
Do the same to the other colours: 2 x 3 = 6 and 5 x 3 = 15
Add together 6, 9 and 15 - the answer is 30 which is correct.