A) \[17\frac{6}{7}\,\,\text{km/h}\]
B) \[35\,\,\text{km/h}\]
C) \[25\text{ km/h}\]
D) \[30\,\,\text{km/h}\]
Correct Answer: B
Solution :
1 h 40 min 48 s = 1 h \[\left( 40+\frac{48}{60} \right)\]min = 1 h \[\left( 40+\frac{4}{5} \right)\]min \[=1\,\,\text{h}\frac{204}{5}\]min \[=\left( 1+\frac{204}{300} \right)\,\,\text{h=}\frac{504}{300}\text{h}\] \[\therefore \] Speed \[=\frac{42}{\frac{504}{300}}=25\,\,\text{km/h}\] \[\therefore \] \[\frac{5}{7}\times \]Usual speed = 25 \[\therefore \] Usual speed \[=\frac{25\times 7}{5}=35\,\,\text{km/h}\]
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