100人中7位って英語でなんて言うの？

When referring to your position amongst a quantity of people, you can refer to yourself as, for example "7th out of 100 people". This particular applies to a race where you may have come seventh place out of 100 people who ran the race, or you may have been 7th in the class of 100 students with the highest score.

You would phrase this in a few different ways. The most common of these two examples is the first one, "i came 7th out of 100 people". If for example you wanted to include some more information about what you were taking part in you could add it on the end.
e.g. I came 7th out of 100 people in a long distance race.

You can use the verbs of "placed", "got", or "won" to talk about the placing you achieved in a competition.

In any competition...we are " placed". IE We come first / second / third / fourth /
fifth / sixth ...or in this case seventh (7th) in consecutive order...
(Out of the number of participants) We can say here ; "I came 7th" out of 100.

Well done! Seventh may not be a gold, silver or bronze position but it is a very respectable result.
'...out of..' is a construction used when you wish to state your position compared to the total number of people taking part.

If you finished at number 7 in the competition involving 100 people, it means that you finished the competition in the 7th place. Finishing a competition at number 7 out of 100 competitors is not bad at all compared to someone who finishes at number 50 (50th place) out of 100 people. You must be proud of yourself even though you did not finish at number 1(1st place) or number 2 (2nd place) or number 3 (3rd place).
So, you may say:
I came 7th out of 100 competitors.
or
I finished 7th out of 100 runners.

If you are in a competition and you are 7th from 100 people, the most common way of expressing this is that you came 7th. Sometimes you will also hear the expression about 7th place or I placed 7th out of 100 people.

Colloquially you may also hear people say 'I got 7th' though I find this informal and wouldn't use it in a business setting.