Who knows how to do this problem? There is a 240 km long river. Ship a runs upstream and ship B runs downstream at the same time, and meets at the midpoint. After meeting, the two ships continue to sail, and meet for the second time at 40 km away from the midpoint when they return. It takes three hours from the first meeting to the second meeting to find the speed of the two ships in still water

Who knows how to do this problem? There is a 240 km long river. Ship a runs upstream and ship B runs downstream at the same time, and meets at the midpoint. After meeting, the two ships continue to sail, and meet for the second time at 40 km away from the midpoint when they return. It takes three hours from the first meeting to the second meeting to find the speed of the two ships in still water

The speed of two ships in still water x, y, water velocity V it takes 3 / 2 time for two ships to travel the whole course together, the whole course = 3 (x + V + Y-V) / 2 = 3 (x + y) / 2 and the whole course = 240, so 240 = 3 (x + y) / 2x + y = 160 meet at the midpoint, then: x + V = y-vv = (Y-X) / 2x + V = x + (Y-X) / 2 = (x + y) / 2 = 160 / 2 = 80x-v = x - (Y-X) / 2 = (3x-y)

When a shopping mall sells a commodity, its profit margin increases by 8 percentage points because the purchase price is 6.4% lower than the original purchase price?

Let the original purchase price be a yuan, and the original profit rate of this commodity be X. according to the equation, a (1 + x) − a (1 − 6.4%) a (1 − 6.4%) = x + 8%, and the solution is x = 17%

A question about fraction application
A car drives to the destination 180km away from the starting place. After the first hour of departure, it accelerates to 1.5 times of the original speed, and arrives at the destination 40 minutes earlier than the original plan. The average driving speed of the previous hour is calculated

If the average driving speed in the previous hour is V, and the vehicle reaches its destination in t hours after accelerating, then
v+1.5vt=180
v（1+t+2/3)=180
t=4/3h,v=60Km/h

A fraction problem!
x^2+y^2+z^2
-----------------If x = 1 and X, y, Z are not equal to 0, prove 1 / x + 1 / y + 1 / z = 0
(x+y+z)^2
(if you can't play semicolon, just make do. And I'm a junior high school student.)

(x^2+y^2+z^2)/ x+y+z)^2=1(x^2+y^2+z^2 )/(x^2+y^2+z^2+2xy+2xz+2yz)=1x^2+y^2+z^2=x^2+y^2+z^2+2xy+2xz+2yz2xy+2xz+2yz=0xy+xz+yz=0(xy+xz+yz)/xyz=01/x + 1/y +1/z=0