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At the banquet, two people shook hands one by one, a total of 28 times, asked: how many people in total? Such as the title! Requirements: with a quadratic equation solution!
If there are x people to attend the banquet, then each person should shake hands with the remaining X-1 people separately, then a total of X (x-1) times of shaking hands will be needed. However, because a and B shake hands the same as B and a, this number will be divided by two. So [x (x-1)] 2 = 28, 1 / 2x & sup2; - 1 / 2x-28 = 0 X & sup2; - x-56 = 0 factor points
Mathematical problems in stamps
1. How many kinds of postage can you pay if you get a stamp of 4, 8 and 10? What do you think?
2. There are several stamps of 4, 8, 10, 20 and 90 points. If you want to take out 40 points stamps, you can design several schemes
3. According to the regulations of the postal department, the postage is 1.20 yuan for each 20g letter (less than 20g is calculated as 20g). How much is the postage for a 30g letter?
4. The postage for each 20g letter in other districts is 1.20 yuan. How much is the postage for Zhang Yang's 75g letter?
1. Like the following combination
One: 4, 8, 10
Two: 4 + 8 = 12, 4 + 10 = 14, 8 + 10 = 18
One: 4 points + 8 points + 10 points = 22 points
2. Single species: 4 points x 10, 8 points x 5, 10 points x 4, 20 points x 2
Two kinds: 4 points x2 + 8 points x4, 4 points X4 + 8 points X3, 4 points X6 + 8 points X2, 4 points X8 + 8 points x1
4 points x 5 + 10 points x 2, 4 points x 5 + 20 points x 1, 10 points x 2 + 20 points x 1
Three kinds: 4 points X1 + 8 points x2 + 10 points X2, 4 points X1 + 8 points x2 + 20 points x1
4 points X3 + 8 points X1 + 10 points X2, 4 points X3 + 8 points X1 + 20 points x1
3.30/20 = 1:10, 1.2x (1 + 1) = 2.4 yuan
4.75/20 = 3,15,1.2x (3 + 1) = 4.8 yuan
How many times do 40 students shake hands to greet each other
40 * 39 / 2 = 780 times
RELATED INFORMATIONS
- 1. How many times do 20 students shake hands to greet each other?
- 2. There is a party of ten students. If each of them shakes hands with the others, how many times?
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