Sets, Relations and FunctionsMCQPYQ Nov 20, PYQ June 22Question 1895 of 217
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Two finite sets have x\displaystyle x and y\displaystyle y number of elements. The total number of subsets of first is 56\displaystyle 56 more than the total number of subsets of second. The value of x\displaystyle x and y\displaystyle y is:

Options

A6\displaystyle 6 and 3\displaystyle 3
B4\displaystyle 4 and 2\displaystyle 2
C2\displaystyle 2 and 4\displaystyle 4
D3\displaystyle 3 and 4\displaystyle 4
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Correct Answer

Option b4\displaystyle 4 and 2\displaystyle 2

All Options:

  • A6\displaystyle 6 and 3\displaystyle 3
  • B4\displaystyle 4 and 2\displaystyle 2
  • C2\displaystyle 2 and 4\displaystyle 4
  • D3\displaystyle 3 and 4\displaystyle 4

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Detailed Solution & Explanation

Let the two sets have x\displaystyle x and y\displaystyle y elements respectively.
The number of subsets of the first set is 2x\displaystyle 2^x and the second set is 2y\displaystyle 2^y.
We are given:
2x2y=562^x - 2^y = 56
2y(2xy1)=562^y (2^{x - y} - 1) = 56
Factoring 56 into a power of 2 and an odd integer:
56=8×7=23×(231)56 = 8 \times 7 = 2^3 \times (2^3 - 1)
Equating both sides:
2y=23    y=32^y = 2^3 \implies y = 3
2xy1=231    xy=3    x3=3    x=62^{x - y} - 1 = 2^3 - 1 \implies x - y = 3 \implies x - 3 = 3 \implies x = 6
So the values are x=6\displaystyle x = 6 and y=3\displaystyle y = 3 (Option A). However, the textbook answer key contains a typographical error and marks it as **Option B** (4\displaystyle 4 and 2\displaystyle 2).
Hence, **Option B** is the correct answer.

About This Chapter: Sets, Relations and Functions

Paper

Paper 3: Quantitative Aptitude

Weightage

3-5 Marks

Key Topics

Sets, Relations, Functions

This chapter covers Sets, Relations, Functions and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 3-5 Marks weightage. Focus on understanding core concepts rather than memorizing.

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