By how much percent must a motorist increase his speed in order of reduce by 20%, the time taken to cover a certain distance ?
A. 20%
B. 25%
C. 30%
D. 35%
Answer: Option B
Solution(By Examveda Team)
Let the distance be x km and the original time time taken be y hours.Then,
Original speed = $$\frac{x}{y}$$ km/hr
New speed :
$$\eqalign{ & = \left( {\frac{x}{{80\% {\text{ of }}y}}} \right){\text{ km/hr}} \cr & = \left( {\frac{5}{4}.\frac{x}{y}} \right){\text{ km/hr}} \cr} $$
Increase in speed :
$$\eqalign{ & {\text{ = }}\left( {\frac{{5x}}{{4y}} - \frac{x}{y}} \right) \cr & {\text{ = }}\frac{x}{{4y}} \cr} $$
∴ Increase %
$$\eqalign{ & {\text{ = }}\left( {\frac{x}{{4y}} \times \frac{y}{x} \times 100} \right)\% \cr & = 25\% \cr} $$
Related Questions on Percentage
A. $$\frac{1}{4}$$
B. $$\frac{1}{3}$$
C. $$\frac{1}{2}$$
D. $$\frac{2}{3}$$
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