A) 45 min
B) 60 min
C) 48 min
D) 120 min
Correct Answer: B
Solution :
[b] Let original speed and time be S and T, respectively. Then, \[S\times T=\frac{3}{4}S\times \left( T+\frac{20}{60} \right);\] \[\frac{4}{3}T=\left( T+\frac{1}{3} \right)\] \[\Rightarrow \] \[\frac{4}{3}T-T=\frac{1}{3}\] \[\Rightarrow \] \[\frac{T}{3}=\frac{1}{3}\] \[\Rightarrow \]\[T=1\,h=60\min \] |
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