Mathematics · Probability

JEE Main 2026 — 21 January, Morning Shift — Question 13

Let the mean and variance of 7 observations 2,4,10,x,12,14,y,x>y2,4,10, \mathrm{x}, 12,14, \mathrm{y}, \mathrm{x}>\mathrm{y}, be 8 and 16 respectively. Two numbers are chosen from {1,2,3,x−4,y,5}\{1,2,3, \mathrm{x}-4, \mathrm{y}, 5\} one after another without replacement, then the probability, that the smaller number among the two chosen numbers is less than 4 , is:

  1. Option A:

    35\frac{3}{5}

  2. Option B:

    45\frac{4}{5}

    Correct
  3. Option C:

    25\frac{2}{5}

  4. Option D:

    13\frac{1}{3}

Answer: B

Step-by-step solution

Mean (x‾)=8(\overline{\mathrm{x}})=8 (Given)

⇒2+4+10+x+12+14+y7=8\Rightarrow \frac{2+4+10+x+12+14+y}{7}=8

⇒x+y=14……\Rightarrow \mathrm{x}+\mathrm{y}=14 \ldots\ldots Variance (σ2)=16\left(\sigma^{2}\right)=16 (Given)

⇒16=22+42+102+x2+122+142+y27−82\Rightarrow 16=\frac{2^{2}+4^{2}+10^{2}+\mathrm{x}^{2}+12^{2}+14^{2}+\mathrm{y}^{2}}{7}-8^{2}

⇒x2+y2=100\Rightarrow \mathrm{x}^{2}+\mathrm{y}^{2}=100 (2).....

∵(x+y)2=x2+y2+2xy\because(x+y)^{2}=x^{2}+y^{2}+2 x y

⇒xy=48\Rightarrow \mathrm{xy}=48 (sum is 14 product is 48 )

Since problem states x>yx>y

∴x=8\therefore \mathrm{x}=8 and y=6\mathrm{y}=6

Now set X={1,2,3,4,6,5}X=\{1,2,3,4,6,5\}

Now we choose two numbers one after author without replacement total outcomes =6×5=30=6 \times 5=30

We want the prob.

That the smaller number among the two is less than 4 P(\mathrm{P}( smaller <4)=1−P(<4)=1-\mathrm{P}( smaller ≥4)\geq 4) =1−630=45=1-\frac{6}{30}=\frac{4}{5}

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Mathematics
Chapter
Probability
Topic
Mean, variance, expected values of distributions
Let the mean and variance of 7 observations 2,4,10, x , 12,14, y , x… | JEE Main 2026 PYQ with Solution · DhiX AI