One by three plus three by five plus five by seven plus Add bracket two n minus one bracket two N plus one?

One by three plus three by five plus five by seven plus Add bracket two n minus one bracket two N plus one?

n/(2n+1)

How many natural numbers can be filled in the brackets of one seventh, five thirds and one third?

Turn all the molecules into five
That is to say, 1 / 7 and 1 / 3 are both numerator and denominator multiplied by 5
So 5 / 35

I'm eager for the detailed answer of (3.7% 3) × (3.7% 1) - (7.3% 1) × 22% 7 × 22% 21!

(3 / 7) × (3 / 7) - (7 / 3) × 7 / 22 × 21 / 22
=（24/7）×（22/7）-（22/3）×（7/22）×（21/22）
=528/49 -49/22
=11616/1078-2401/1078
=9215/1078