Fill in the missing parts of the 100 explain this to me so i can explain to my little i’m in 11th and he’s in second so the fact that i have no clue how to do this is really sad

A "100 chart" is a listing of all the numbers 1 to 100, in rows of 10. This results in columns of numbers that all end in the same digit. For your purpose of instructing your little brother, I recommend you web-search for "100 chart" and print one of the ones available.

Locating the given numbers on a "100 chart", you find they are in the last 4 columns of the rows ending in 20, 30, 40, 50. Overlaying the boxes onto the chart, you see they correspond to number positions ...

  17 _ _ 20

  27 _ 29 _

  _ 38 _ 40

  47 _ _ 50