# What does this sentence mean?(About it and which)

We follow the same principle, but using only a small sample of words (around 120) to achieve the same result. Among all the words you check in the second step, we find which word (say, #55) has the same number of blank checkboxes before it (say, 18), as it has checked boxes after it (again, 18). We then look up the frequency rank of this "midpoint" word #55, which turns out to be #15,000, which means that you know 15,000 words.

Here is my question:What I can't understand is " we find which word (say, #55) has the same number of blank checkboxes before it (say, 18), as it has checked boxes after it (again, 18)."..Mainly I don't understand "which" and "it" mean what.

And the previous paragraph is ------To understand how we come up with the exact number at the end, let's start with an analogy. Imagine you have the whole dictionary of 45,000+ words, with words arranged in order from most-common to least-common, and you mark all the words you know. At the end, you go back, and discover that at exactly word #15,000, there are 2,000 words that came earlier (more common words) which you didn't know. And at word #15,000, there are 2,000 words which come afterwards (less common words) which you do know. The 2,000 after which you do know cancel out the 2,000 before you don't, and in the end it means you know 15,000 words.

• Was this description accompanied by any visual sample of the "checkboxes" it mentions? Also, please search definitions for "which" and state which definition applies to your example (hint, hint). – Brian Hitchcock Jul 4 '15 at 12:10
• yeah..I am doing a vocabulary test which needs to click checkboxes if you know the word.I've edited the question. – vankee Jul 4 '15 at 13:58
• Suppose that they give you 100 words, and you're supposed to check the checkbox before each word you know. And suppose that you've checked 37 words, not necessarily consecutively, there will be a word which if you count only the checked words, has 18 words before it and 18 words after it. This word is what they call "midpoint", and in their example, it was mentioned as word #55 (of those 100 words, perhaps). If this #55 word is the 15000th word on their list, they will tell you that you know (approximately) about 15000 words. – Damkerng T. Jul 4 '15 at 14:11
• But what does say and again mean in (say, 18) and (again,18)? – vankee Jul 4 '15 at 16:36
• I seem to misread the passage. It says that word #55 has 18 unchecked words before it and 18 checked words after it. -- The words say and again refer back to the number (of unchecked/checked boxes/words): say, 18 means "let's say the number of blank checkboxes before it (word #55) is 18"; again, 18 means "which, again, there are 18 checked boxes after it (word #55)". – Damkerng T. Jul 4 '15 at 17:22