If we subtract thrice a certain number from each of the two terms of the ratio , the ratio becomes . Find the number.
Use to write an equation between the old and new ratios.
Recall that if we subtract thrice a certain number from , then it can be written as .
So, if we subtract thrice a certain number from 33 and 19, then they can be written as and .
Now, , , 3, and 10 are proportional:
Cross-multiply to find :
Therefore, the number is 13.