100 Liters of water is available equally in a month for consumption among 5 members @ 1 dollar per liter. If some members don't use their own available 20 liters, it can be used by the others at the same rate. (for example, if a member uses only 5 liter in that month, their remaining 5 liters can be used by others at $1). In a particular month, the usage was as follows:

A - 25 liters

B - 5 liters

C - 17 liters

D - 40 liters

E - 33 liters

The additional 20 liters was purchased at $10 per liter after the initial 100 liters were consumed disproportionately. How do you calculate individual water cost of each member?


closed as off-topic by ffao, Apep, NL628, Rubio Apr 13 '18 at 21:50



  • 1
    $\begingroup$ This seems more like a homework problem than a puzzle in the recreational sense. $\endgroup$ – Jeff Zeitlin Apr 13 '18 at 18:39
  • $\begingroup$ Honestly, its a real life problem more than a home work. Numbers are toned down to understand the issue. $\endgroup$ – Viraj Apr 13 '18 at 18:40
  • $\begingroup$ I'm not sure what is the goal of the puzzle. Are we trying to distribute the costs in a certain way (such as a "fair" distribution that minimizes the differences between costs)? Or can we suggest any way of distributing the water usage? If so, that would result in many different answers. $\endgroup$ – MikeQ Apr 13 '18 at 18:46
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    $\begingroup$ This may be a real life problem, but it is not a puzzle. It's just mechanical application of arithmetic, once you decide on a method of allocating the excess expense. If your goal is to get us to give you that method, it's still not a puzzle, but now it's too broad and/or primarily opinion based. Which close reason do you prefer? :) $\endgroup$ – Rubio Apr 13 '18 at 18:46
  • $\begingroup$ Sounds like a dispute which should be in "Relationships", maybe with some more information on the personalities and existing agreements. This isn't math nor a puzzle. $\endgroup$ – Dark Matter Apr 13 '18 at 20:10

My guess:

Everyone below 20 l pays the 1-dollar-per-l rate, so B pays 5 and C 17. Their excess 18 l would then be distributed equally across the group, making 26 l available to A, D, and E at 1-dollar-per-l. That means A pays 25, leaving 0.5 l for D and E. I will presume that costs for halves would be distributed equally, so D pays 26.5 + 10*13.5 or 161.50, and E pays 26.5 + 10*6.5, or 91.50.

