a) 24 km
b) 26 km
c) 21 km
d) \[23\frac{{23}}{{59}}\] km
Answer: d
Explanation:
$$\eqalign{
& {\text{Average}}\,{\text{speed}} \cr
& = \frac{{{\text{total}}\,{\text{distance}}\,{\text{covered}}}}{{{\text{total}}\,{\text{time}}}} \cr
& {\text{Total}}\,{\text{Distance}} = {16 + 20 + 10} \cr
& = 46\,{\text{km}} \cr
& {\text{Time}}\,{\text{taken}} = {\frac{{16}}{{20}}} + {\frac{{20}}{{40}}} + {\frac{{10}}{{15}}} \cr
& = {\frac{{4}}{{5}}} + {\frac{{1}}{{2}}} + {\frac{{2}}{{3}}} \cr
& = {\frac{{24 + 15 + 20}}{{30}}} \cr
& = \frac{{59}}{{30}} \cr
& {\text{Average}}\,{\text{speed}} \cr
& = \frac{{46 \times 30}}{{59}} \cr
& = 23\frac{{23}}{{59}}\,{\text{km/hr}} \cr} $$
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