Answer:
a. 0
Explanation:
Rounding fractions:
For a fraction a/b if a/b ≥ 1/2 then round up else round down
9/10 > 1/2 so round up to 1. We can show this by multiplying denominator and numerator of 1/2 by 5 => 5/10
Since denominators are equal, just compare the numerators
9/10 vs 5/20; 9 > 5 so 9/10 > 5/20 => 9/10 > 1/2
Similarly 8/10 can be rounded up to 1
So the estimate of
9/10 - 8/10 = 1 - 1 =0
Answer a. 0