Fill in the question mark according to the rule

23 19 21 17 15 17? Every two groups, that is: (23 19) (21 17) (19 15) (17 13), the rule is: the number after is the number before - 4, so "?" is 13.25 27 27 29 31? Every two groups, that is, (25 27) (27 29) (29 31) (31 33)

RELATED INFORMATIONS

1. For a rope, 20% of the total length is used for the first time, and half of the total length is used for the second time, with 4.5m left. How long is the rope?
2. For a rope, cut 25% in the first time, and cut 5 meters less in the second time than in the first time. This is 25 meters left. How many meters are there in the whole court?
3. A rope, the first minus 38, the second minus the remaining 15, there are still 24 meters, how long is this rope?
4. A rope, the first cut 38, the second cut 14, there are 24m left, how long is this rope?
5. A rope, the first minus 38, the second minus the remaining 15, there are still 24 meters, how long is this rope?
6. As shown in the picture, the gold medal used in Beijing Olympic Games has a diameter of 70mm, the diameter of the center circle is 30mm, and the width of the gold medal's border is 5mm. Can you calculate the area of the ring-shaped jade wall inlaid on the back of the medal?
7. A project, Party A and Party B cooperate to complete in 8 days. Party A did it alone for 6 days, Party B did it alone for 5 days, a total of 27 / 40 of this project. If this project is done by Party A alone, how many days will it take to complete?
8. In the first half of 2004, China imported about 18.04 million tons of steel, accounting for 39 / 40 of the steel imports in the first half of 2003
9. In a 12 cm long, 6 cm wide rectangular piece of paper, cut a 1 cm radius disc, you can cut up to () discs
10. 1. Three out of eighty-six / one out of eighty-seven 2. An engineering team built a highway. 38m in the first day, 42m in the second day. The second day more than the first day was 1 / 28 of the total length of the road. How many meters in the total length of the road? How many parts of the road were built in the two days 3. Two jackets with the original price of 1200 yuan were sold in the shopping mall. It is known that one of them earned 1 / 5 and the other lost 1 / 5. What are the current prices of these two jackets? (there must be a formula, and you'd better answer it) 4. There are two boxes of fruit. 3 / 5 of the weight of box a is equal to 3 / 4 of box B. what is the weight of Box B? (write the answer directly) 5. To make a part, it takes 5 minutes for a, 7 minutes for B, and 1 / 4 of every minute for C. among the three people, () is the most effective 6. Read a science and technology book, read 1 / 6 of it every day, and finish 1 / 2 of the book in () days 7. When the value of x equals () or (), X2 = 6x 8.1/30 + 1 / 42 + 1 / 56 + 1 / 72 + 1 / 90 Those who answer all the above questions will consider adding! /On behalf of the division sign, answer to mark the question number!
11. This is the question 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9. + 100 =?
12. If 1 = 5, 2 = 6, 3 = 7, 4 = 8, then 5 =? Answer Such as the title
13. What's the next number?
14. Mathematics problems (fractional equation) Set up fractional equation to solve the problem: the design speed of Fuzhou Third Ring Road is 80 per hour. It is known that the distance between a and B is 20 km. Xiao Zhang walks along the Third Ring Road at an average speed of 80 per hour, which is 15 minutes shorter than the original speed. Find out Xiao Zhang's original speed. (the distance between a and B is 20 km when taking the original road and the third ring road.)
15. There are 140kg flour in two bags a and B. If 12.5% of the flour in bag a is put into bag B, the weight of flour in the two bags will be the same. How many kg flour are there in the two bags? (please list the detailed formula and use the equation to solve it) ≮ if you answer this question within 3 days,
16. 1. For a project, team a will do it alone for 15 days, team B will do it alone for 20 days, team a will do it alone for 5 days, and team a and team B will do it together for several days. A total of 4 / 5 of the whole project will be completed? 2. The task of processing a batch of parts directly from one car is completed by the first group in 20 days, and by the second group in 30 days. Now, it is done by the second group for 6 days, and then by the combination of one and two for 3 days. The rest is completed by the first group. How many days will it take? 3. For a pond, it takes 20 hours to operate a single pump, 30 hours to operate B single pump, and 15 hours to operate C single pump?
17. （）÷﹙﹚＝﹙﹚÷﹙﹚＝﹙﹚÷﹙﹚＝6
18. There is a batch of goods. One quarter of the goods were transported on the first day, and three fifths on the second day. There are still 90 tons left to be transported. How many tons are there? 2. The road construction team is working on a highway. One quarter of the highway is built on the first day, and the remaining two thirds are built on the second day. It is known that a total of 1200 meters are built in these two days. How many meters is the whole highway?
19. Xiao Ming's money to buy a pen is 5 yuan, Xiao Hong's money to buy a pen is 2 yuan, two people buy a pen more than one yuan, how much is a pen?
20. Given that the solution of X − 1x + 2 − XX − 1 = m (x + 2) (x − 1) is negative, try to find the value range of M