what's 1/3 of 20000?

'of' represents multiplication,

so,  1/3 × 20000

we can write 20000 as-

20000/1

Now, simply multiply fractions,

1/3 × 20000/1 = 1×20000/3×1

                        = 20000/3

                        = 6666.6666  or 6666.7