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JEE Advanced 2022 Paper 1 · Mathematics · Permutations and Combinations · hard

Match the counting statements in List-I with the numbers in List-II. List-I (P) Number of real solutions of |x^2-4|=x+2 (Q) Number of ordered pairs…

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Match the counting statements in List-I with the numbers in List-II.

List-I
(P) Number of real solutions of ∣x2−4∣=x+2|x^2-4|=x+2
(Q) Number of ordered pairs (m,n)(m,n) of positive integers with 1m+1n=16\dfrac1m+\dfrac1n=\dfrac16
(R) Number of three-digit numbers divisible by 77 whose digits add up to 1010
(S) Number of real solutions of sin⁡x=x4π\sin x=\dfrac{x}{4\pi}

List-II
(1) 77
(2) 33
(3) 99
(4) 88
(5) 66
  1. A. P→2, Q→3, R→1, S→4
  2. B. P→3, Q→2, R→4, S→1
  3. C. P→2, Q→3, R→4, S→1
  4. D. P→2, Q→5, R→4, S→1
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Answer: (C) P→2, Q→3, R→4, S→1

(P) x2−4=x+2x^2-4=x+2 gives x=−2,3x=-2,3; x2−4=−(x+2)x^2-4=-(x+2) gives x=−2,1x=-2,1; the distinct solutions are −2,1,3-2,1,3: three (2). (Q) (m−6)(n−6)=36(m-6)(n-6)=36 with both factors positive (negative factors would give m<6m<6 or n<6n<6 and are impossible since 1m<16\frac1m<\frac16 is required): τ(36)=9\tau(36)=9 pairs (3). (R) Multiples of 77 with digit sum 1010: 154,217,280,343,406,532,721,910154,217,280,343,406,532,721,910: eight (4). (S) Solutions need ∣x∣≤4π|x|\le4\pi. For x>0x>0: one crossing in (0,π)(0,\pi), and two in (2π,3π)(2\pi,3\pi) where the hump of height 11 exceeds the line value at most 34\frac{3}{4}; none beyond. That gives 33 positive, 33 negative and x=0x=0: seven (1). So P→2, Q→3, R→4, S→1.
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