A math problem is worth 100 points When a ship sails between a and B, it takes 3 hours to go downstream and 30 minutes more to go upstream than it does downstream. It is known that the speed of the ship in still water is 26 kilometers per hour. Find the speed of the current and the distance between a and B

A math problem is worth 100 points When a ship sails between a and B, it takes 3 hours to go downstream and 30 minutes more to go upstream than it does downstream. It is known that the speed of the ship in still water is 26 kilometers per hour. Find the speed of the current and the distance between a and B

Let the velocity be X
The velocity against the water is equal to ship velocity velocity = 26-x
The speed along the water is equal to ship speed + velocity = 26 + X
The downstream time is 3 hours, so the upstream time is 3 hours + 30 minutes = 3.5 hours
So the distance between a and B = 3 (26 + x) = 3.5 (26-x)
78+3x=91-3.5x
6.5x=13
x=2
So the velocity of the water is 2 kilometers per hour
Distance between the two places = 28x3 = 84km

1 math problem 100 points!
ab/a+b=3
ca/c+a=4
bc/b+c=5
ab+bc+ac/abc=
Why

ab/a+b=3
ca/c+a=4
bc/b+c=5
1/a+1/b=1/3
1/c+1/a=1/4
1/b+1/c=1/5
Add up,
2(1/a+1/b+1/c)=47/60
1/a+1/b+1/c=47/120
ab+bc+ac/abc
=1/c+1/a+1/b
=47/120

Three math questions, 100 points for good answers
The railway between Beijing and Taiyuan is 1100 km long. At 10 am, a passenger train leaves Beijing for Taiyuan at the speed of 75 km / h; at 14 PM, a train leaves Taiyuan for Beijing at the speed of 85 km / h?
The railway between Beijing and Taiyuan is 1180 kilometers long. At 9 a.m., a passenger train goes from Beijing to Taiyuan at the speed of 75 km / h; at 13 noon, a train goes from Taiyuan to Beijing at the speed of 85 km / h?
There is a 5.6dm high and 4.4dm & sup3; rockery in a fish tank. If the water pipe injects water into the fish tank at a flow rate of 15 cubic decimeters per minute, how many minutes will it take to make the rockery completely submerged?
I'm sorry, the third one raised a question
The bottom of the fish tank is 4.6dm long and 2.5dm wide

1) T is the time from 14:00 to meet. 75 × (14-10) + T × (75 + 85) = 1100, the solution is t = 5h, so the two cars meet at 19:00. 2) 75 × (13-9) + T × (75 + 85) = 1180, the solution is t = 5.5h, the solution is 18.5:00. 3) suppose it takes X minutes. X * 15 = 5.6 * 4.6 * 2.5-4.4, the solution is x = 4

If f (x) is an odd function with period π, then f (x) can be ()
A. sinxB. cosxC. sin2xD. cos2x

A. F (x) = SiNx, ∵ ω = 1, ∵ t = 2 π, which is odd function, which is not suitable for the problem; B, f (x) = cosx, ∵ ω = 1, ∵ t = 2 π, which is even function, which is not suitable for the problem; C, f (x) = sin2x,