IMO it is advisable to remember fractional value of 2,3,4,5,6,7,8,9 at least for the test bcoz these type of q are ment to eat your time.
other methods needs some smart way to calcukate like round off equally in the numerator and equally in the denominator.as
[1.3(rounded off to 1 dec place)*.7*1.1]/.8*.8*.8=1.001/.512= again round off gives 1000/500[approx]=2
but if options are very close then this method may lead to a wrong ans.
but in any case do the whole multiplication only if u are able to finish it in time of 1.5 min.
It does not matter how many times you get knocked down , but how many times you get up