There are () different ways to write 40 as the sum of two primes A. 2B. 3C. 4D. 5

There are () different ways to write 40 as the sum of two primes A. 2B. 3C. 4D. 5

According to the definition of prime number, 40 = 3 + 37 = 11 + 29 = 17 + 23, there are three different ways to write it

Please write two formulas for the four numbers 3,4, - 6 and 10 in three different ways, so that the result is exactly equal to 24
I don't want the answer. I know the answer. I want to ask a question like this. How can I find it?

1. Use 3 × 8 = 24, 4 × 6 = 24 to solve
If 3, 3, 6 and 10 can form (10-6 ／ 3) × 3 = 24, or 2, 3, 3 and 7 can form (7 + 3-2) × 3 = 24, etc. practice has proved that this method has the highest utilization rate and hit rate
2. Using the operation characteristics of 0 and 11
For example, 3, 4, 4 and 8 can form 3 × 8 + 4-4 = 24, and 4, 5, J and K can form 11 × (5-4) + 13 = 24
3. In the group of cards with solutions, the most widely used are the following six solutions: (we use a, B, C, D to represent the four numbers on the card surface)
①(a—b）×（c＋d）
Such as (10-4) × (2 + 2) = 24, etc
②（a＋b）÷c×d
Such as (10 + 2) △ 2 × 4 = 24, etc
③（a－b÷c）×d
Such as (3-2 △ 2) × 12 = 24, etc
④（a＋b－c）×d
Such as (9 + 5-2) × 2 = 24, etc
⑤a×b＋c—d
For example, 11 × 3 + L-10 = 24, etc
⑥（a－b）×c＋d
Such as (4-L) × 6 + 6 = 24, etc
Game, students may wish to try in accordance with the above methods
It should be noted that: after accurate calculation by computer, 4 cards can be randomly selected from a deck (52 cards), and there are 1820 different combinations, among which 458 card groups can not calculate 24 points, such as a, a, a, 5
It is not difficult to see that "skillfully calculating 24 points" can greatly mobilize the eyes, brain, hands, mouth and ears

How many different ways can 60 be written as the sum of two prime numbers?

3+57
7+53
13+47
17+43
19+41
23+37
29+31
There are seven

Write 34 as the sum of two primes, and you can write () addition expressions

3+31
5+29
11+13
Three

The product of the reciprocal of two prime numbers is 1 / 65. What are the two numbers?

If the product of the reciprocal of two prime numbers is 1 / 65, then the product of the two prime numbers is 65
And 65 = 5 × 13
5 and 13 are prime numbers, so they are 5 and 13 respectively
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The product of the reciprocal of two prime numbers is one in 65. How many are the two prime numbers? For the specific process, I will offer him 10 rewards!

How do you do
Because 1 / 65 = 1 / 5 × 1 / 13
So these two prime numbers are 5 and 13

The product of two prime numbers is 65. What is the sum of their reciprocal? How to find the algorithm?

6 PINK sweetheart 6,
65＝5×13
1/5＋1/13＝18/65

The sum of the reciprocal of a pair of prime numbers is 18 out of 65. What is the product of the reciprocal of the two prime numbers?
Write the process

18 / 65 is divided, so 65 = 13 * 5 18 = 13 + 5 is the product of the reciprocal of 13 and 5, which is 1 / 65

If there is such a prime number, it is still a prime number if he adds 13 and 17 respectively

It's impossible
We know: odd + odd = even odd + even = odd
13 and 17 are odd, even number only 2 is prime, 2 is smaller than 13 and 17, so we can't add odd number
Even numbers can be added. Add a 2. But 13 + 2 = 15, 15 is a composite number, so it doesn't hold
So it's impossible

If the set of all prime numbers within 1 -- 20 is C, then C = {2,3,5,7,11,13,17,19}

Prime. Refers to a natural number greater than 1, in addition to 1 and the integer itself, can not be divided by other natural numbers
And the set in C conforms to prime numbers within 1-20!