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A. The distance between city B is 1000 km. The two trains of a and B start from city a and B at the same time and run in opposite directions. They meet on the way. Car a arrives at place B 15 hours after meeting, and car B arrives at place a 6 + 2 / 3 hours after meeting. If the speed of car B is 1.5 times that of car a, the speed of car a and car B should be calculated (set up equations to solve practical problems)
Let the speed of car a be x and that of car B be 1.5x
15X+(6+2/3)*1.5X=1000
15X+9X+X=1000
25X=1000
X = 40 (km / h)
Speed of car B: 1.5x = 40 * 1.5 = 60 (km / h)
A: the speed of car a is 40 km / h, and that of car B is 60 km / h
The two trains a and B leave each other from the two cities at the same time. When car a travels 36 kilometers less than car B, the two trains are 264 kilometers apart. Given that the speed ratio of car a and B is 5:6, how many kilometers are the two cities apart
Let B travel for X kilometers, then a travel for (x-36) kilometers. From the meaning of the title, we can get that: X − 36x = 56 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 6x-216 = 5x & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 216216 × 2-36 + 264 = 660 (kilometers). A: the two cities are 660 kilometers apart
The distance between city a and city B is 560 km. The two trains leave from city a and city B at the same time and meet in 3.5 hours. Car a travels 85 km per hour, and how many km per hour does car B travel?
560 △ 3.5-85, = 160-85, = 75 (km); answer: car B travels 75 km per hour
42 students went on an outing. Each student drank a bottle of mineral water, which was 2 yuan per bottle. They bought 6 bottles for free. How much did it cost at least?
The answer is 72 yuan, I know. The question is how to explain it to the third grade students
Hello, 916201327
Buy 6 and get 1 free bottle, which is equivalent to buying 6 bottles with the money
6 + 1 = 7 (bottle)
There are 7 bottles in each group, and 42 bottles are as follows:
42 △ 7 = 6 (Group)
Each group only needs to spend:
6 × 2 = 12 yuan
The total cost is at least:
6 × 12 = 72 yuan
Two cars a and B start from two places 360 kilometers apart at the same time. After 4 hours, they meet on the way. The speed ratio of car a to car B is 5:4
How many kilometers per hour?
50km/h
Let car a be x, then car B be 0.8x
360/（X+0.8X）=4
X=50
The calculation of the second radical of the eighth grade mathematics
The root sign is the square
（√7+√3-2√2-3√5）（√7-3√5+2√2-√3）
(√7+√3-2√2-3√5)(√7-3√5+2√2-√3)
=[(√ 7-3 √ 5) + (√ 3-2 √ 2)] [(√ 7-3 √ 5 √) - (√ 3-2 √ 2)] use the square difference formula
=(√ 7-3 √ 5) &# 178; - (√ 3-2 √ 2) &# 178; using the complete square formula
=7-6√35+45-3+4√6-8
=41-6√35+4√6
If each vehicle carries 3 tons of goods, there will be 5 tons left. If each vehicle carries 4 tons, there will be 5 less vehicles. How many vehicles are there and how many tons of goods are there
Vehicles, goods
With X cars, the solution is: 3x + 5 = (X-5) * 4 x = 25 3 * 25 + 5 = 80 A: there are 25 cars and 80 tons of goods
How much does it cost at least if each of the six fourth grade teachers takes 78 students to make friends?
2 yuan a bottle, buy ten get one free, 45 yuan a box, 10% off
Outing!
Buy ten get one free, and the price of each bottle is 2 × 10 / 11 = 20 / 11
One case is 24 bottles, the unit price of each bottle is 45 × 0.9/24 = 27 / 16
The unit price of packing is lower
So we need to buy (78 + 6) / 24 = 3, and the remainder is 12
You need to buy 10 bottles and get 11 bottles
One more bottle is enough
The total amount is 45 × 0.9 * 3 + 2 * 10 + 2 = 143.5 yuan
1. Two cars a and B set out from two places 360 kilometers apart and went opposite. After 4 hours, they met on the way. It is known that the speed ratio of car a to car B is 5
4. How many kilometers does car a travel per hour? (two algorithms)
2. The road repair team built a road. In the first week, it built 3 / 8 of the total length of the road, and in the second week, it built 2 / 5 of the rest of the road. There are still 90 kilometers left. How many kilometers is the total length of the road?
Hurry! Hurry!
You have to use both
(1) Method 1: the sum of the two vehicle speeds is 360 / 4 = 90 km / h. 90 / (5 + 4) = 10, so the speed of a is 5 * 10 = 50 km / h. method 2: suppose the speed of a is 5x, then the speed of B is 4x. 4 * (5x + 4x) = 360x = 10, so the speed of a is 10 * 5 = 50 km / h. (2) the second week, we repaired: (1-3 / 8) * 2 / 5 = 1 / 4, total length =
The root is ┲ (because I can't play)
Q: why is 3 / (┲ 6 + ┲ 3) + 1 / (┲ 3 + ┲ 2) = ┲ 6 - ┲ 2
That is how to get the result
3/（√6 + √3 ） + 1/（√3+ √2）
=3（√6 -√3 ）/[（√6 + √3 ）（√6 -√3 ）]+（√3- √2）/[（√3+ √2）(√3- √2）]
=3（√6 -√3 ）/[6-3]+（√3- √2）/[3-2]
=（√6 -√3 ）+（√3- √2）
=√6 - √2
Original formula = radical 6-radical 3 + radical 3-radical 2
Rationalizing the denominator
Very simple! Will the denominator be rationalized? If so, it will come out!
3 / (┲ 6 + ┲ 3) and multiply by ┲ 6 - ┲ 3
3/（┲6 + ┲3 ）=┲6 - ┲3
The numerator denominator of 1 / (┲ 3 + ┲ 2) is multiplied by ┲ 3 - ┲ 2 at the same time
1 / (┲ 3 + ┲ 2) = ┲ 3 - ┲ 2 add up to OK
De denominator
Rationalize the denominator
Original formula = 3 / (√ 6 + √ 3) + 1 / (√ 3 + √ 2)
=3(√6-√3)/[(√6+√3)*(√6-√3)]+(√3-√2)/[(√3+√2)*(√3-√2)]
=3(√6-√3)/(6-3)+(√3-√2)/(3-2)
=(√6-√3)+(√3-√2)
=√6-√2
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