Question

delete

Answer 1

@jim_thompson5910 just two more problems that I am stuck on!

Answer 2

How many coins are you selecting?

Answer 3

alright, one sec

Answer 4

Are you sure you can select any number of coins you want? Is it supposed to be 3 or 4?

Answer 5

I am really sorry! It is suppose to be 3!

Answer 6

ok one sec

Answer 7

What?

Answer 8

hold on

Answer 9

There are 9 C 3 = 84 different ways to choose 3 coins where the order doesn't matter


Now let's count the number of ways to make less than 25 cents.


If you select a quarter first, then you are not less than 25. So that's out. The first coin must either be a nickel or a dime.


---------------------------------------------------------------------------------------------------------------------------------------

If the first coin is a dime, then here are the following ways to get 25 cents:


dime, dime, quarter

dime, dime, dime

dime, dime, nickel


where order doesn't matter


The only way to get under 25 cents is to have 2 additional nickels: dime, nickel, nickel


There are (5 C 1)*(3 C 2) = 5*3 = 15 ways to get under 25 cents with 3 coins (where the first coin is a dime)

---------------------------------------------------------------------------------------------------------------------------------------

If the first coin is a nickel, then the same idea is applied and these choices give you totals under 25 cents:

nickel, nickel, dime

nickel, nickel, nickel


There are (3 C 2)*(5 C 1) + 3 C 3 = 3*5 + 1 = 16 ways to do this.


====================================================================================================================================================================================


Add up the previous counts:

15+16 = 31


So there are 31 ways to add up the coins to get under 25 cents.


So there are 84 - 31 = 53 ways to get 3 coins to add to 25 cents or more.

Answer 10

It is saying that's wrong!!

Answer 11

That was just an example for choosing 3 coins. We are still waiting to see if the number of coins is specified.

Answer 12

hmm let me think

Answer 13

Sorry, you already said that 3 coins are drawn, right?

Answer 14

8?

Answer 15

wait, no sorry, thinking..

Answer 16

There are 10 coins in all.
Choose 3 out of 10 is 10C3=120.
Subtract those under 15 = 5C1*3C2 we get 105.

Answer 17

It turns out that the answer is 108, but I have no idea how it is 108

Answer 18

Oops, subtract NNN as well, so that makes 104, not quite 108.