double counting

huynh anh phuong

12/12/2017 at 10:59

There are many people in the party, in the party has 4 tables, each tables have 3 plates, each plates has 9 pancakes. How many people in the party?

double counting

Lê Quốc Trần Anh Coodinator 29/12/2017 at 18:00

The title is missing some information: Each person has a pancake.

So there are: \(4.3.9=108\left(people\right)\) in the party.
FA Liên Quân Garena 30/12/2017 at 21:44

The title is missing some information: Each person has a pancake.

So there are: 4.3.9=108(people)

in the party.
nguyen tuan anh 06/04/2018 at 13:48

the title is missing some information : Each person has a pancake

so there are : 4.3.9 = 108 (people) in the party

Đỗ Phi Phi

26/07/2017 at 21:39

Votes Answers Follow

A prime number is called a jillyprime when doubling it and adding 1 results in another prime. How many numbers lass than 15 are jillyprimes? (Note that 1 is not a prime.)

Prime Numbers and Composite Numbers double counting adding

Phan Thanh Tinh Coodinator 26/07/2017 at 23:34

2 x 2 + 1 = 5

3 x 2 + 1 = 7

5 x 2 + 1 = 11

7 x 2 + 1 = 15

11 x 2 + 1 = 23

13 x 2 + 1 = 27

So,there are 4 jillyprimes which are less than 15 : 2 ; 3 ; 5 ; 11
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FA KAKALOTS 28/01/2018 at 22:04

2 x 2 + 1 = 5

3 x 2 + 1 = 7

5 x 2 + 1 = 11

7 x 2 + 1 = 15

11 x 2 + 1 = 23

13 x 2 + 1 = 27

So,there are 4 jillyprimes which are less than 15 : 2 ; 3 ; 5 ; 11

A house has 10 rooms. Ten boys stay in different rooms and count the number of doors in them. After that they sum all results and receive 25. What a proposition can't be true about number N of doors which led outside the house?

double counting

tth 30/10/2017 at 15:14

We have:

25 do not divide to 10

So 25 can't be true about number N of doors .

Note: I'm not certain
Ma Kết 05/04/2018 at 14:42

We have:

25 do not divide to 10

So 25 can't be true about number N of doors .

Note: I'm not certain
Ma Kết 05/04/2018 at 14:41

Hà Đức Thọ

falcon handsome moderators

09/03/2017 at 12:34

Votes Answers Follow

Let the answer be k . We count the total number of paris of students were on duty together in the k days. Since every pair of students was on duty together exactly once, this is equal to \(C^{15}_2\) x 1 = 105. On the other hand, since 3 students were on duty per day, this is also equal to \(C^3_2\) x k = 3k. Hence 3k = 105 and so k = 35

double counting