Question 490219
EXP:

take one glass has 100 ml coffee and another glass 100 ml water.

take 10 ml coffee from 1st one  and mix into the second one .and now take 10 ml mixture from second one and mix into the first one .then finally 1st one have 90.90909 ml coffee and second one have 90.90909 ml water.

c) There is as much coffee in the first tumbler as there is water in the second tumbler.