## Oil Tanker Problem

### 06 09 2015

**Introduction**

Last night I was finishing off some work when I came across a problem on a help site: the problem had been posted in December 2014 and hadn’t been answered. I realise that 9 months is a long time but I wanted to understand the problem and see if I could provide a solution: I did both!

One of the difficulties with the problem as stated was that the questioner asked for a nested IF solution, He insisted. Other people tried to help him and he duly provided a mock up of his worksheet for us all. Again he talked about a nested IF statement solution and even provided one … that he freely admitted didn’t work.

The problem is this:

- there are two oil storage tanks and oil is first measured by means of a dip stick which is then used to estimate the amount of oil in the tanks
- the oil is stored for days at a time and each day new oil is added
- every now and again, though, the tanks are drained

He said that by taking the differences between opening and closing stocks for each day he can estimate the amount of oil added; and by adding together the results for the two tanks he gets overall additions for a day.

Good!

Then he says the problem comes when the tanks are drained … his calculation shows a negative result for dranage day!

I translated his graphic into a worksheet and here it is.

The question is: can you solve his problem?

This table starts in B7 and in L11 there is a formula: =E11-E10+H11-H10

That formula is then filled down to the end of the table, day 31 in cell L41

You can see the problem clearly in the second part of the table, day 27 , where they have drained the first tank overnight:

That’s it: I solved this problem … can you? Let me know and I will share my solution. If you ask, you must tell me what you did to try to solve it. No try, no get! 😉

Duncan Williamson

06 09 2015 at 6:43 pm

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