a) \(\displaystyle{1 \over 2}\) giờ = \(\displaystyle{5 \over 10}\) giờ;
\(\displaystyle{4 \over 5}\) giờ = \(\displaystyle{8 \over 10}\) giờ
Ta có: \(\displaystyle{5 \over {10}} < {8 \over {10}}\) suy ra \(\displaystyle{1 \over 2} < {4 \over 5}.\)
Vậy \(\displaystyle{4 \over 5}\) giờ dài hơn \(\displaystyle{1 \over 2}\) giờ.
b) \(\displaystyle{2 \over 3}m = {{10} \over {15}}m\;;\;\;\;{3 \over 5}m = {9 \over {15}}m.\)
Ta có \(\displaystyle{{10} \over {15}} > {9 \over {15}}\) suy ra \(\displaystyle{2 \over 3} > {3 \over 5}.\)
Vậy đoạn \(\displaystyle{3 \over 5}\) mét ngắn hơn \(\displaystyle{2 \over 3}\) mét.
c) \(\displaystyle{6 \over 7}kg = {{48} \over {56}}kg\;;\;\;\;{7 \over 8}kg = {{49} \over {56}}kg.\)
Ta có \(\displaystyle{{48} \over {56}} < {{49} \over {56}}\) suy ra \(\displaystyle{6 \over 7} < {7 \over 8}\).
Vậy \(\displaystyle{7 \over 8}\) kilôgam lớn hơn \(\displaystyle{6 \over 7}\) kilôgam.
