EquationsPYQ May 25Question 4005 of 155
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Puru gets on the elevator at the 11th floor of a building and rides up at the rate of 57 floors per minute. At the same time, Ishu gets on an elevator at the 51st floor of the same building and rides down at the rate of 63 floors per minute. If they continue travelling at these rates, then at which floor will their paths cross?

Options

A17
B19
C27
D30
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Correct Answer

Option d30

All Options:

  • A17
  • B19
  • C27
  • D30

Detailed Solution & Explanation

Let t\displaystyle t be the time in minutes after they start riding the elevators.
1. **Puru's position**:
Puru starts at the 11th\displaystyle 11^{\text{th}} floor and rides up at a rate of 57\displaystyle 57 floors per minute. His floor position at time t\displaystyle t is given by:
FP=11+57tF_P = 11 + 57t
2. **Ishu's position**:
Ishu starts at the 51st\displaystyle 51^{\text{st}} floor and rides down at a rate of 63\displaystyle 63 floors per minute. Her floor position at time t\displaystyle t is given by:
FI=5163tF_I = 51 - 63t
Their paths will cross when they are on the same floor, i.e., FP=FI\displaystyle F_P = F_I:
11+57t=5163t11 + 57t = 51 - 63t
Add 63t\displaystyle 63t to both sides and subtract 11\displaystyle 11 from both sides:
57t+63t=511157t + 63t = 51 - 11
120t=40120t = 40
t=40120=13 minutest = \frac{40}{120} = \frac{1}{3} \text{ minutes}
Now, substitute the value of t\displaystyle t back into either floor equation to find the crossing floor:
F=11+57(13)=11+19=30F = 11 + 57 \left(\frac{1}{3}\right) = 11 + 19 = 30
Alternatively, using Ishu's equation:
F=5163(13)=5121=30F = 51 - 63 \left(\frac{1}{3}\right) = 51 - 21 = 30
Hence, they cross at the 30th\displaystyle 30^{\text{th}} floor.
Hence, **Option D** is the correct answer.

About This Chapter: Equations

Paper

Paper 3: Quantitative Aptitude

Weightage

4-6 Marks

Key Topics

Linear, Quadratic and Cubic Equations

This chapter covers Linear, Quadratic and Cubic Equations and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 4-6 Marks weightage. Focus on understanding core concepts rather than memorizing.

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