Hi All!!
I was looking over some practice problems but I couldn't find the answers to them. So I was wondering if you guys can help me (Studying).
(I'm going to apologize ahead of time because it might be a long post)
How many 5-digit briefcase combinations contain
1. Two pairs of distinct digits and 1 other distinct digit. (e.g 12215)
I wasn't sure on which approach was correct.
10 * 9 * 8 (because there are three distinct digits)
or
10C2 * 5C2* 3C2 * 8 (because you have to take into account how the doubles can be orientated)
2. A pair and three other distinct digits. (e.g 27421)
same issue as above
10*9*8*7
or
(5C2*10) * 9 * 8 * 7
I have found this question before but I couldn't get an explanation:
2.How many ways are there to pick a collection of 12 coins from piles of pennies, nickels, dimes, quarters, and half-dollars? Base on the following condition:
a. there are only 10 coins in each pile.
16C4 - 5^2 because it's the total minus how many ways I can get from the 11th coin and the 12th coin. = 1795
b. There are only 10 coins in each pile and the pick must have at least one penny and two nickels?
1795 - 13C4(?)
my logic is that it's because 12-3+4 C 4 but I'm not sure if I have to set it to 12 or 10.
Lastly,
1.Let B subset A and f : B subset Abe a 1-1 and onto, then B = A
( Sets A and B can be either finite or infinite.)
T?
2. A simple graph G with 13 vertices has 4 vertices of degree 4, 3 vertices of degree 3 and 6 vertices of degree 1, then G must be a tree.
T?
3.The spanning tree for any given graph is always unique.
F?
4.(A Union B subset A union C) then B subset C.
T?
5.Let A and B be nonempty sets and f: A->B be a function. Then if f(x n y) = f(x) n f(y) for
all nonempty subsets X and Y of A, then f must be 1-1.
T?
Thank you! (If you help me I WILL LOVE YOU FOR THE REST OF MY LIFE)
Hello, yummytree!
How many 5-digit briefcase combinations contain
1. Two pairs of distinct digits and 1 other distinct digit. (e.g 12215)
We have the digits: in some order.
There are 10 choices for the , 9 choices for the , 8 choices for the
The digits can be arranged in: ways.
Answer: .
2. A pair and three other distinct digits. (e.g 27421)
We have the digits:
There are: 10 choices for the , 9 choices for the ,
. . 8 choices for the , 7 choices for the
The digits can be arranged in: ways.
Answer: .