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JEE Main 20198 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
8 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Statistics

JEE Main 2019 · 8 April · Morning Shift · Mathematics · Statistics

The mean and variance for seven observations are 8 and 16...

The mean and variance for seven observations are 88 and 1616 respectively. If 55 of the observations are 2,4,10,12,14,2, 4, 10, 12, 14, then the product of the remaining two observations is

Options

  1. A4848
  2. B4545
  3. C4949
  4. D4040

Correct answer

A. 4848

Step-by-step solution

Let the remaining two observations are xx and yy.

Mean x¯=∑xiN=2+4+10+12+14+x+y7\overset{¯}{x} = \dfrac{∑ {x}_{i}}{N} = \dfrac{2 + 4 + 10 + 12 + 14 + x + y}{7}

⇒42+x+y7=8⇒ \dfrac{42 + x + y}{7} = 8

⇒x+y=14...(1)⇒ x + y = 14 . . . \left(1\right)
Variance,

σ2=∑xi2N−(x¯)2=4+16+100+144+196+x2+y27−64{\sigma}^{2} = \dfrac{∑ {x}_{i}^{2}}{N} - {\left(\overset{¯}{x}\right)}^{2} = \dfrac{4 + 16 + 100 + 144 + 196 + {x}^{2} + {y}^{2}}{7} - 64

⇒σ2=460+x2+y27−64=16⇒ {\sigma}^{2} = \dfrac{460 + {x}^{2} + {y}^{2}}{7} - 64 = 16

⇒x2+y2=100…⇒ {x}^{2} + {y}^{2} = 100 \ldots\left(2\right)</p><p>From(1)</p><p>From \left(1\right) and \left(2\right),weget,</p><p>, we get,</p><p>x = 6, y = 8andandxy = 48

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