A person covers a certain distance at 40 km/hr. If he increases his speed by 4 km/hr, he reaches 6 minutes earlier. How much time does he take at his original speed?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 66 min
The distance is the same at both speeds, so the difference of the two times is the 6 minutes saved. This gives the distance, and then the time at 40 km/hr.
New speed \(=40+4=44\) km/hr; 6 minutes \(\displaystyle =\frac{1}{10}\) hour
\(\displaystyle \frac{D}{40}-\frac{D}{44}=\frac{1}{10}\), that is \(\displaystyle \frac{44D-40D}{1760}=\frac{1}{10}\)
\(4D=176\), so \(D=44\) km
Time at 40 km/hr \(\displaystyle =\frac{44}{40}=1.1\) hours \(=66\) minutes