the question said use the method of halving the interval to find AN approximation...
this doesnt' neccessarily mean an approximation with one try of the halving interval or with two tries or with three tries or whatever...
because this is not specified, both answers are acceptable.
correct to one decimal place is the most stupid thing i have ever heard for a question like that, which has a root between 0.7 and 0.9... wtf
and, yeah, as for myself, i did it once, got 0.75 and thought nothing of doing it twice, so put o.8 as my answer to 1 d.p.
but seriously, that question is a joke, and noone should fret about whether it is 0.7 or 0.8. The only reason I put 0.8 and did it once was cos it just didn't seem right to put 0.7 as an approximation to a root "between" 0.7 and 0.9