The average of 16 and x is 21. Find x. The average of 2 numbers is the sum of the 2 numbers divided by 2. So we have: (16 + x)/2 = 21 Cross multiply: 16 + x = 21*2 16 + x = 42 To solve this equation, we type this expression into the search engine and get x = 26. Check our work by restating our answer: The average of 16 and 26 is 21. TRUE.