A man rows at 15 kmph in still water. Downstream where current is 3 kmph, how long to cover 60 metres?
Show answer Hide answer
Answer: D. 12 seconds
Explanation
Adding the still water speed of fifteen to the current speed of three yields a downstream speed of eighteen kilometers per hour. Converting eighteen kilometers per hour into meters per second gives five meters per second. Dividing the distance of sixty meters by five meters per second results in a travel time of twelve seconds. Downstream speed is calculated by combining the velocity of a watercraft in still water with the speed of the river current. Unit conversion from kilometers per hour to meters per second requires multiplying by five-eighteenths. Speed, distance, and time are related through basic kinematic formulas governing uniform motion.
Option A suggests ten seconds, which would require a faster speed than the calculated five meters per second. Option B proposes fifteen seconds, underestimating the velocity achieved by combining the boat and current speeds. Option C offers twenty seconds, resulting from an incorrect division or unit conversion calculation step.
- Subject
- Mathematics
- Category
- Mathematics
- Topic
- —
- Difficulty
- medium
Related questions
Q1. A circle sector has a 21 cm radius and a 135° central angle. Find its perimeter.
Show answer Hide answer
Answer: A. 91.5 cm
Calculating the arc length of the sector using one thirty fifth over three hundred sixty gives forty nine point five. Adding the two bounding radii lengths of forty two centimeters to the arc length gives ninety one poin...
Q2. What is the smallest fraction that exactly divides 6/7, 5/14, and 10/21_________?
Show answer Hide answer
Answer: A. 30/7
Finding the smallest fraction that divides a set of fractions requires dividing the least common multiple. The calculation involves determining the least common multiple of the numerators and greatest common divisor. Exe...
Q3. What is the smallest number which leaves remainders of 14, 19, 29, and 34 when divided by 20, 25, 35, and 40 respectively________?
Show answer Hide answer
Answer: C. 1349
Subtracting each remainder from its respective divisor consistently yields a uniform difference value of six. Finding the least common multiple of all the specified divisors yields a baseline value of one thousand four h...
Q4. A boat travels at 60 kmph in still water with a 20 kmph current. Find its downstream and upstream speeds.
Show answer Hide answer
Answer: B. 80, 40 kmph
Downstream speed is calculated by adding the still water speed and the current speed together. Adding sixty kilometers per hour and twenty kilometers per hour yields an exact downstream speed of eighty. Upstream speed is...
Q5. A motorboat's speed-to-current ratio is 36:5. Traveling downstream for 5 hours 10 minutes, how long will the return trip take_______?
Show answer Hide answer
Answer: C. 6 hours 50 min
Assigning algebraic variables to the motorboat speed and current determines downstream and upstream velocities. Equating the distance traveled in both directions allows calculating the required return journey duration. C...
Q6. A sum under compound interest triples in 3 years. In how many years will it increase to 9 times its original value?
Show answer Hide answer
Answer: D. 6
Compound interest causes financial sums to grow geometrically over regular fixed time interval periods. If a sum triples every three years, tripling it again multiplies the original principal by nine total times. Multipl...