Math: extremely tricky question! logic needed

http://www.admissionstests.cambridgeasse…

how would i go about doing question 25, without a calculator, in under two minutes?

:) word explanations along side mathematical ones would be highly appreciated!

In the first, there are 90ml if both, so he effectively takes 45 ml each in the 90ml which he removes. In B, there are now (120+45)ml oil and (60+45)ml vinegar (or 165o and 105v)
He takes 90ml, or 1/3 of the flask. This equates to 55o and 35v, leaving (165-55)ml of oil, or 110o.
55 + the 45 left in the first = 100ml of oil and 110ml in the second

C