'a' means that you have left 10 minutes in some process. e.g. The busy schedule just left 10 minutes with me to have my dinner
'b' means you have only 10 minutes remaining for some work to be completed. e.g. I just have 10 minutes left to complete this work
Both can be modified to mean the same thing. If you have further doubts, kindly let me know.
October 9, 2012
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