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Mathematics Test - 28
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Mathematics Test - 28
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  • Question 1/10
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    A pair of dice is thrown. Find the probability of obtaining a sum of 8 or getting an even number on both the dice.

    Solutions

    Let the events be defined as:

    A: Obtaining a sum of 8

    B: Getting an even number on both dice

    Now cases favourable to A are \((3,5)(5,3)(2,6)(6,2)(4,4)\)

    So, \(P(A)=\frac{5}{36}\)

    Cases favourable to B: \((2,2),(2,4),(2,6),(4,2),(4,4),(4,6),(6,2),(6,4),(6,6)\)

    P(B)=\(\frac{9}{36}\)

    Now, \((2,6)(6,2)\) and \((4,4)\) are common to both events \(A\) and \(B\)

    So, \(P(A \cap B)=\frac{3}{36}\)

    \(\Rightarrow P ( A \cup B )=\frac{5}{36}+\frac{9}{36}-\frac{3}{36}\)

    \(\Rightarrow P ( A \cup B )\)\(=\frac{11}{36}\)

  • Question 2/10
    1 / -0

    Evaluate: \(\int_{1}^{4}\left(5 x^{2}-8 x+5\right) d x\)

    Solutions

    Given,

    \(\int_{1}^{4}\left(5 x^{2}-8 x+5\right) d x\)

    Let, \(I=\int_{1}^{4}\left(5 x^{2}-8 x+5\right) d x\)

    \(I=\int_{1}^{4}\left(5 x^{2}\right) d x-\int_{1}^{4} 8 x . d x+\int_{1}^{4} 5 d x\)

    Using, \(\int^{n} d x=\frac{1}{n+1} x^{n+1}+c\)

    \(I=5 \int_{1}^{4} x^{2} d x-8 \int_{1}^{4} x d x+5 \int_{1}^{4} d x\)

    \(I=5\left[\frac{x^{3}}{3}\right]_{1}^{4}-8\left[\frac{x^{2}}{2}\right]_{1}^{4}+5[x]_{1}^{4}\)

    \(I=5\left[\frac{4^{3}-1^{3}}{3}\right]-8\left[\frac{4^{2}-1^{2}}{2}\right]+5[4-1]\)

    \(=5 \times \frac{63}{3}-8 \times \frac{15}{2}+5 \times 3\)

    \(=60\)

  • Question 3/10
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    The equation of circle which passes through the origin and cuts off intercepts 5 and 6 from the positive parts of the \(x\) axis and \(y\) -axis respectively is \(\left(x-\frac{5}{2}\right)^{2}+(y-3)^{2}=\lambda\), where \(\lambda\) is:

    Solutions

    From figure, we have

    \(P=5, O Q=6\)

    and \(O M=\frac{5}{2}, C M=3\)

    \(\therefore\) ln \(\Delta O M C, O C^{2}=O M^{2}+M C^{2}\)

    \(\Rightarrow  O C^{2}=\left(\frac{5}{2}\right)^{2}+(3)^{2} \Rightarrow O C=\frac{\sqrt{61}}{2}\)

    Thus, the required circle has its centre \(\left(\frac{5}{2}, 3\right)\)

    and radius \(\frac{\sqrt{61}}{2}\).

    So, its equation is \(\left(x-\frac{5}{2}\right)+(y-3)^{2}=\left(\frac{61}{4}\right)\).

    Thus, \(\lambda=\frac{61}{4}\)

  • Question 4/10
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    In a quadrilateral \(PQRS , \overrightarrow{ PQ }=\overrightarrow{ a }, \overrightarrow{ QR }=\overrightarrow{ b }, \overrightarrow{ SP }=\overrightarrow{ a }-\overrightarrow{ b }\). \(M\) is the mid-point of \(QR\) and \(X\) is a point on \(SM\) such that \(SX =\frac{4}{5} SM\), then \(\overrightarrow{ PX }\) is:

    Solutions

    Choose \(P\) as the origin of the reference.

    \(\overrightarrow{ PR }=\vec{a}+\vec{b}\)

    \(\overrightarrow{ PS }=-(\vec{a}-\vec{b})=\vec{b}-\vec{a}\)

    \(\overrightarrow{ PM }=\overrightarrow{ a }+\frac{\overrightarrow{ b }}{2}\)

    Given:\(\overrightarrow{ SX } =\frac{4}{5}\overrightarrow{ SM }\)

    \(\overrightarrow{ PX }-(\overrightarrow{ b }-\overrightarrow{ a })=\frac{4}{5}\left\{\overrightarrow{ a }+\frac{\overrightarrow{ b }}{2}-(\overrightarrow{ b }-\overrightarrow{ a })\right\}\)

    \(\overrightarrow{ PX }=\frac{3}{5}\overrightarrow{ a }-(-\frac{6}{10}\overrightarrow{ b })\)

    \(\Rightarrow \overrightarrow{ PX } =\frac{3}{5}(\overrightarrow{ a }+\overrightarrow{ b })\)

    \(=\frac{3}{5} \overrightarrow{ PR }\)

  • Question 5/10
    1 / -0

    The equations of the sides of a triangle are x - 3y = 0, 4x + 3y = 5 and 3x + y = 0. The line 3x - 4y = 0 passes through the _________ of the triangle.

    Solutions

    Let line L1: x – 3y = 0 …(i)

    L2: 4x + 3y = 5 …(ii)

    L3: 3x + y = 0 …(iii)

    The slope of L1, m1 =13

    The slope of L2, m2 =-43

    The slope of L3, m3 = -3

    Here, m1m3 = -1

    So, L1 is perpendicular to L3.

    Let L: 3x – 4y = 0

    Slope, m =34

    Here, m2m = -1

    So, L is perpendicular to L2.

    The line L passes through the origin and it is perpendicular to L2.

    So, L will pass through the orthocentre.

  • Question 6/10
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    How many numbers between \(100\) and \(1000\) can be formed with the digits \(5,6,7,8,9,\) if the repetition of digits is not allowed?
    Solutions

    Number lying between \(100\) and \(1000\) formed by \(3\) digits.

    And every digit have \(5\) option \((1,2,3,4,5)\) to select a number.

    But repetition is not allowed.

    So, number \(={ }^{5} P_{3}\)

    \(=\frac{5 !}{(5-3) !}\)

    \(=\frac{5 !}{2 !}\)

    \({ }^{5} P_{3}\)\(=60\)

  • Question 7/10
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    \(A , B\) and \(C\) are three mutually exclusive and exhaustive events. \(P ( A )=2 P ( B )=6 P ( C )\), Find \(P ( B )\):

    Solutions

    Given,\(P(A)=2 P(B)=6 P(C)\)

    We know that when events are mutually exclusive and exhaustive,

    \(P(A)+P(B)+P(C)=1\)

    Let, \(P(A)\) = \(k\)

    Then, \(P(B)= \frac{P(A)}{2}=\frac{k}{2}\)

    \(P(B)=\frac{k}{2}\)

    \(\Rightarrow P(C)= \frac{k}{6}\)

    So, according to the concept\(k+\frac{k}{2}+\frac{k}{6}=1\)

    \(\Rightarrow \frac{10 k}{6}=1\)

    \(\Rightarrow k=\frac{3}{5}\)

    Therefore,\(P(B)\) = \(\frac{k}{2}=\frac{3}{5 \times 2}\)\(=0.3\)

  • Question 8/10
    1 / -0

    A plane passes through the point \((1,-2,3)\) and is parallel to the plane \(2 x-2 y+z=0 .\) The distance of the point \((-1,2,0)\) from the plane is:

    Solutions

    Let the parallel plane to \(2 x-2 y+z=0\) is \(2 x-2 y+z+\lambda=0\)

    It passes through \((1,-2,3)\)

    \(\therefore 2+4+3+\lambda=0\)

    \(\Rightarrow \lambda=-9\)

    The distance of \((-1,2,0)\) from the plane

    \(2 x-2 y+z-9=0\) is \(\left|\frac{-2-4-9}{\sqrt{5+4+1}}\right|=\left|\frac{-15}{3}\right|=5\)

  • Question 9/10
    1 / -0

    Using principle of mathematical induction, prove that for \(n \in N\), \(3^{2 n+2}-8 n-9\) is:

    Solutions

    Given:

    \(\mathrm{P}(\mathrm{n})=3^{(2 \mathrm{n}+2)}-8 \mathrm{n}-9=8 \mathrm{~m}\)

    Where \(\mathrm{a} \in \mathrm{N}\), i.e. a is a natural number.

    For \(\mathrm{n}=1\)

    \(\text { LHS }=3^{(2 \times 1+2)}-8 \times 1-9 \)

    \(=3^{4}-17 \)

    \(=81-17 \)

    \(=64=8 \times 8\)

    Therefore, \(\mathrm{P}(\mathrm{n})\) is true for \(\mathrm{n}=1\)

    Suppose, \(\mathrm{P}(\mathrm{k})\) is true.

    \(3^{(2 k+2)}-8 k-9=8 a\).....(1) [where \(\mathrm{a} \in \mathrm{N}\)]

    Now, we will prove that \(\mathrm{P}(\mathrm{k}+1)\) is true.

    \(\text { LHS }=3^{2(\mathrm{k}+1)+2}-8(\mathrm{k}+1)-9 \)

    \(=9\left[3^{(2 \mathrm{k}+2)}\right]-8 \mathrm{k}-17\)

    From equation (1), we get

    \(=9[8 \mathrm{a}+9+8 \mathrm{k}]-8 \mathrm{k}-17 \)

    \(=72 \mathrm{a}+64 \mathrm{k}+64 \)

    \(=8(9 \mathrm{a}+8 \mathrm{k}+8) \)

    \(=8 \mathrm{~b}\)

    Where \(\mathrm{b}=9 \mathrm{a}+8 \mathrm{k}+8\) and \(\mathrm{b}\) is natural number.

    Therefore, \(\mathrm{P}(\mathrm{k}+1)\) is true whenever \(\mathrm{P}(\mathrm{k})\) is true.

    Therefore, \(\mathrm{P}(\mathrm{n})\) is true for \(\mathrm{n}\), where \(\mathrm{n}\) is a natural number.

    So, the given equation is divisible by 8.

  • Question 10/10
    1 / -0

    Let \(\mathrm{f}:[-1,3] \rightarrow \mathrm{R}\) be defined as

    \(f(x)=\left\{\begin{array}{cc} |x|+[x], & -1 \leq x<1 \\ x+|x|, & 1 \leq x<2 \\ x+[x], & 2 \leq x \leq 3 \end{array}\right.\)

    where \([t]\) denotes the greatest integer less than or equal to \(t\). Then, \(\mathrm{f}\) is discontinuous at:

    Solutions

    Given function is,

    \(f(x)=\left\{\begin{array}{cc} |x|+[x], & -1 \leq x<1 \\ x+|x|, & 1 \leq x<2 \\ x+[x], & 2 \leq x \leq 3 \end{array}\right. \)

    \(=\left\{\begin{array}{cc} -x-1, & -1 \leq x<0 \\ x, & 0 \leq x<1 \\ 2 x, & 1 \leq x<2 \\ x+2, & 2 \leq x<3 \\ 6, & x=3 \end{array}\right. \)

    \(\Rightarrow\)\(\begin{array}{c} f(-1)=0, f\left(-1^{+}\right)=0 \end{array} \)

    \(f\left(0^{-}\right)=-1, f(0)=0, f\left(0^{+}\right)=0 \)

    \(f\left(1^{-}\right)=1, f(1)=2, f\left(1^{+}\right)=2 \)

    \( f\left(2^{-}\right)=4, f(2)=4, f\left(2^{+}\right)=4 ; \)

    \(f\left(3^{-}\right)=5, f(3)=6\)

    \(\mathrm{f}(\mathrm{x})\) is discontinuous at \(\mathrm{x}=\{0,1,3\}\)

    Hence, \(\mathrm{f}(\mathrm{x})\) is discontinuous at only three points.

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