u can work out the expectation before attempting the question if u dunno the ans.
Assuming the question has 4 options and u r totally clueless about it, the expectation of the mark u will obtain will be (-0.125)
if u r able to eliminate one option leaving behind 3 that u r unsure of, the expectation will be 0.. so u r indifference between answering or leaving the question blank.
if u are able to eliminate 2 option, den the expectation will be 0.25 and hence u sld attempt the question.
lol... i jus showed u one of the application of probability