the excercise goes like" there are 20 books on the lowest shelf, 18 on next one, 16 on next one etc., till the top shelf on which there is 4 books. How many books are on this bookshelf?"
K so bottom has 20 and each time it goes up you the shelf has 2 less books, so to find how many shelves there are. There are 9 shelves so we add the number of books of these 9 shelves 20+18+16+14+12+10+8+6+4=108
THere are 108 books
Hope that helpes srry if took so long i had to get up for a sec :)
