We can solve this easily with proportions. If the tank is 20% full and has 500 gallons in it, when it is 100% full, it will have a proportional amount of water in it:
where the percentages are on the top and the number of gallons is on the bottom of those ratios.
every lamp can connect other lamps ，from the first ，it can connect the other 24 lamps，and then， the second ，can also connect other 24 。but the line between the first and the second is counted twice。
The Martian satellite Phobos travels in an approximately circular orbit of radius 9.4x10^6m with a period of 7 h39 min. Calculate the mass of Mars from this information.
