Clearly, alternatively we add and subtract 10% of a term to obtain the next term of the series.
Thus, 10000 + (10% of 10000)= 11000;
11000 - (10% of 11000) = 9900;
9900 + (10% of 9900) = 10890;
10890 - (10% of 10890) = 9801.
9801 + (10% of 9801) = 9801+980 = 10781.
So, missing term = 10890- (10% of 10890)= 9801.
