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A motor boat whose speed is 18 km/hr in still water takes 1 hour more to go 24 km upstream than to return downstream to the same spot. The speed of the stream is

  • A. 6 km/hr
  • B. 5 km/hr
  • C. 3.5 km/hr
  • D. 4.5 km/hr

Profile image of Aniket Singh
11 Months agoGrade
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1 Answer

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ApprovedApproved Tutor Answer11 Months ago

To find the speed of the stream, we can use the information given about the motorboat's journey upstream and downstream. Let's break it down step by step.

Given Information

  • Speed of the motorboat in still water: 18 km/hr
  • Distance traveled: 24 km
  • Time difference: 1 hour more upstream than downstream

Speed Calculations

Let the speed of the stream be x km/hr.

The effective speed of the boat upstream is (18 - x) km/hr, and downstream it is (18 + x) km/hr.

Time Formulas

The time taken to travel upstream is:

Time upstream = Distance / Speed = 24 / (18 - x)

The time taken to travel downstream is:

Time downstream = Distance / Speed = 24 / (18 + x)

Setting Up the Equation

According to the problem, the time taken upstream is 1 hour more than the time taken downstream:

24 / (18 - x) = 24 / (18 + x) + 1

Solving the Equation

To solve for x, we can cross-multiply and simplify:

  • 24(18 + x) = 24(18 - x) + (18 - x)(18 + x)
  • 24(18 + x) - 24(18 - x) = (18 - x)(18 + x)
  • 48x = 324 - x²
  • x² + 48x - 324 = 0

Finding the Roots

Using the quadratic formula x = [-b ± √(b² - 4ac)] / 2a, where a = 1, b = 48, and c = -324:

x = [-48 ± √(48² + 4 × 324)] / 2

Calculating this gives us two potential solutions for x.

Final Result

After solving, we find that the speed of the stream is 6 km/hr.

Answer

The speed of the stream is A. 6 km/hr.