Of the many problems I could not solve, the one I find the most interesting is the 7- 11 problem.  I have considered many approaches to this problem and I am yet to find a solution.  The problem states the following:

A guy walks into a 7-11 store and selects four items to buy. The clerk at the counter informs the gentleman that the total cost of the four items is \$7.11. He was completely surprised that the cost was the same as the name of the store. The clerk informed the man that he simply multiplied the cost of each item and arrived at the total. The customer calmly informed the clerk that the items should be added and not multiplied. The clerk then added the items together and informed the customer that the total was still exactly \$7.11.

One of the best I have is spreadsheet.  I have multiple sums of four digits add up to 7.11 then multiply them.

Out of all my effort, the only digits that came close are .81, 2.64, 1.67, and 1.99.  However, the product is not 7.11 exactly.  I also considered factoring 71100000 and multiply the four numbers I obtained by 100, but I failed miserably.  As of this moment, it is a problem that I look at from time to time during leisure to jog my memory.

I would like to know if anyone has found a solution for this problem or if you have another approach that you would suggest.  I would appreciate that.  I do not think it was a waste of my effort, however, I do think I could solve with more time.  I think I missing something; it is somewhat bothersome.  Thus, I will take any suggestion to further this problemÕs solution.

This not the only problem I could not solve, but it was the most interesting thing to me.  I find it to be simple yet demanding a lot of thought.  That is why I picked this problem.

This is the spreadsheet I considered

 0.81 2.64 1.67 1.99 7.106545 2.64 1.67 1.99 7.11

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