Question

14) Juliana has saved her pocket money to buy up to 3 fashion magazines. If there are 5 different magazines to choose from, the number of ways she can buy 1, 2 or 3 magazines is:

A) 90
B) 80
C) 25
D) 70
E) 85

Answer 1

if she buys 1 its 5 ways
2 - 5C2 = its 5*4/2 = 10
3 its 5c3 = 5*4*3 / 3*2 = 10

that a total of 25

Answer 2

number of ways she can buy 1 is C(1,5)
number of ways she can buy 2 is C(2,5)
number of ways she can buy 3 is C(3,5)

C(1,5)+C(2,5)+C(3,5)=25

Answer 3

the answer is 85....

Answer 4

which is E.

Answer 5

let's think again

Answer 6

ok - if it depends on the order in which she buys the magazines it is 85
- this wasn't mentioned in the question

in this case its 5 + 5P2 + 5P3 = 5 + 20 + 60 = 85

- permutations not combinatons

Answer 7

this question is under permutations so there should be just a simple way to multiply them but I figured out how it is 85 using nPr, 5P1+5P2+5P3=85 ways.

Answer 8

ur also using the nPr way, how would u do it using just permutations?

Answer 9

nPr means number of permutations of r in n
and = n! / r!

Answer 10

hmm, so it's basically the same?

Answer 11

yea - oh ill check on that formula - not sure if its right

is it correct?

Answer 12

i think it's nPr=n!/(n-r)!

Answer 13

yup - you r right - my memory failed me there

and nCr - n! / r! * (n-r)! right?

Answer 14

a quick way of calculating say 5C2 is
5*4
---
2*1

i.e. number of digits in top and bottom are the same

Answer 15

E.