Question

A number, twice that number, and one-third of that number are added. The result is 20. What is the original number?

Answer 1

Since you only have enough information to write one equation, you should write everything in terms of one variable

n + 2n + 1/3n = 20

3n + 1/3n = 20

10/3 n = 20

n = 6

now lets check our work:

6 + 12 + 2 = 20

so it is true.