Question

you have 20 books and want to make a reading list that has 3 books on it. How many different reading lists can you make? (2 reading lists are different if they have the same books but in a different order

Answer 1

are you sure you can't make it alone?

Answer 2

take me step by step!? lol dont give me the answer!!

Answer 3

imagine a list like this:

Answer 4

so you start writing the first titile of the 20 you have. How many possiblr choices you have?

Answer 5

@ayojenn ?

Answer 6

wait wait im really confused

Answer 7

you could choose any of the 20 books, no? So 20 posibilities, no?

Answer 8

okk right?

Answer 9

i dont get this part tho (2 reading lists are different if they have the same books but in a different order)

Answer 10

it means:
"pirates of caribean", "Conan", "Math"
"Math","pirates of caribean", "Conan"

is not the same list

Answer 11

same books different order, :)

Answer 12

ok i got it, ok so now what do i do?

Answer 13

so after you wrote the 1º title, you only can choose from 19 left for the 2º title you will write. Ok?

Answer 14

hmm ok? so then i chose the 3 one i have 18? then the 4 i will have 17?

Answer 15

rigth. But you just need 3 books

Answer 16

so you stop after 3 title

Answer 17

ok ok then?

Answer 18

then, think like this: When you wrote the 1º tiltle you had 20 possible books to choose from. So there were 20 possible ways your list could start. And for each of this 20 possibilitys the next steps would be same: 19 books in 2º choice, 18 books in 3º choice. So how many possible lists are there possible to make?

Answer 19

im lost.......... like w're suppose to put 3 books in each list right/??

Answer 20

yes

Answer 21

ok but so far we have only have 1 book in each list

Answer 22

:)

Answer 23

ok, imagine a tree again:

Answer 24

so we need to add 2 more books to each list right?

Answer 25

lol ok