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Mathematics Test - 54

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Mathematics Test - 54
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  • Question 1
    1 / -0

    If sec70∘ − cot20∘/2(cosec59∘ − tan31= 2/m, then m is equal to?

    Solution
    \(\frac{\sec ^{2} 70^{\circ}-\cot ^{2} 20^{\circ}}{2\left(\operatorname{cosec}^{2} 59^{\circ}-\tan ^{2} 31^{\circ}\right)}=\frac{2}{m}\)
    \(\Rightarrow \frac{\sec ^{2} 70^{\circ}-\cot ^{2}\left(90^{\circ}-70^{\circ}\right)}{2\left(\operatorname{cosec}^{2} 59^{\circ}-\tan ^{2}\left(90^{\circ}-59^{\circ}\right)\right)}=\frac{2}{m}\)
    \(\Rightarrow \frac{\sec ^{2} 70^{\circ}-\tan ^{2} 70^{\circ}}{2\left(\operatorname{cosec}^{2} 59^{\circ}-\cot ^{2} 59^{\circ}\right)}=\frac{2}{m}\)
    \(\Rightarrow \frac{1}{2}=\frac{2}{m}\left[\sec ^{2} \theta-\tan ^{2} \theta=1\right]\)
    \(\left.\operatorname{cosec}^{2} \theta-\cot ^{2} \theta=1\right)\)
    \(\Rightarrow m=2 \times 2\)
    \(\Rightarrow m=4\)
  • Question 2
    1 / -0

    Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:

    Solution
    Net part filled in 1 hour = (1/5+1/6−1/12) =17/60
    ∴The tank will be full in 60/17 hours
    i.e.,3(9/17) hours
  • Question 3
    1 / -0

    Find the 15th term of the sequence 20, 15, 10 . . . . .

    Solution
    \(\begin{aligned} 15^{\text {th }} \text { term }=& a+14 d=20+14 \times(-5) \\ &=20-70 \\ &=-50 \end{aligned}\)
  • Question 4
    1 / -0

    If log 2 = 0.3010 and log 3 = 0.4771, the value of log5 512 is:

    Solution
    \(\log _{5} 512\)
    \(=\frac{\log 512}{\log 5}\)
    \(=\frac{\log 2^{9}}{\log \left(\frac{10}{2}\right)}\)
    \(=\frac{9 \log 2}{\log 10-\log 2}\)
    \(=\frac{(9 \times 0.3010)}{1-0.3010}\)
    \(=\frac{2.709}{0.699}\)
    \(=\frac{2709}{699}\)
    \(=3.876\)
  • Question 5
    1 / -0

    Ajit has a certain average for 9 innings. In the tenth innings, he scores 100 runs thereby increasing his average by 8 runs. His new average is:

    Solution
    Let Ajit's average be x for 9 innings. So, Ajit scored 9x run in 9 innings.
    In the 10th inning, he scored 100 runs then average became (x+8). And he scored (x + 8) × 10 runs in 10 innings.
    Now,
    ⇒9x+100=10×(x+8)
    or,9x+100=10x+80
    or,x=100−80
    or,x=20
    Newaverage=(x+8)
    =28runs
  • Question 6
    1 / -0

    sinθ + cosθ/sinθ − cosθ = 3,then the value of sin4θ − cosθ is?

    Solution
    \begin{aligned}
    &\frac{\sin \theta+\cos \theta}{\sin \theta-\cos \theta}=3\\
    &\sin \theta+\cos \theta=3 \sin \theta-3 \cos \theta\\
    &\sin \theta=2 \cos \theta\\
    &\text { i. } e . \frac{\sin \theta}{\cos \theta}=\frac{2}{1}\\
    &\tan \theta=\frac{2}{1}=\frac{P}{B}\\
    &\text { we know that, } H=\sqrt{P^{2}+B^{2}}=\sqrt{5}\\
    &\sin \theta=\frac{2}{\sqrt{5}} \text { and } \cos \theta=\frac{1}{\sqrt{5}}\\
    &\therefore \sin ^{4} \theta-\cos ^{4} \theta\\
    &\Rightarrow\left(\sin ^{2} \theta+\cos ^{2} \theta\right)\left(\sin ^{2} \theta-\cos ^{2} \theta\right)\\
    &\Rightarrow 1 \times\left\{\left(\frac{2}{\sqrt{5}}\right)^{2}-\left(\frac{1}{\sqrt{5}}\right)^{2}\right\}\\
    &\Rightarrow \frac{4}{5}-\frac{1}{5}=\frac{3}{5}
    \end{aligned}
  • Question 7
    1 / -0

    If log 27 = 1.431, then the value of log 9 is:

    Solution
    \(\log 27=1.431\)
    \(\Rightarrow \log \left(3^{3}\right)=1.431\)
    \(\Rightarrow 3 \log 3=1.431\)
    \(\Rightarrow \log 3=0.477\)
    \(\therefore \log 9=\log \left(3^{2}\right)\)
    \(=2 \log 3\)
    \(=(2 \times 0.477)\)
    \(=0.954\)
  • Question 8
    1 / -0

    Three unbiased coins are tossed. What is the probability of getting at most two heads?

    Solution
    Getting at most Two heads means 0 to 2 but not more than 2 Here \(\mathrm{S}=\{\mathrm{T} \mathrm{T} \mathrm{T}, \mathrm{TTH}, \mathrm{THT}, \mathrm{HTT}, \mathrm{THH}, \mathrm{HTH}, \mathrm{HHT}, \mathrm{HHH}\}\)
    Let \(E=\) event of getting at most two heads Then \(E=\{T T T, T T H, T H T, H T T, T H H, H T H, H H T\}\)
    \(\therefore P(E)=\frac{n(E)}{n(S)}=\frac{7}{8}\)
  • Question 9
    1 / -0
    If \(x^{2}-3 x+1=0,\) then the value of \(x^{2}+x+\frac{1}{x}+\frac{1}{x^{2}}\) is?
    Solution
    \(a^{2}+b^{2}=5 a b\)
    \(\Rightarrow \frac{a^{2}}{a b}+\frac{b^{2}}{a b}=5\)
    \(\Rightarrow \frac{a}{b}+\frac{b}{a}=5\)
    Squaring the both sides \(\Rightarrow\left(\frac{a}{b}\right)^{2}+\left(\frac{b}{a}\right)^{2}+2 \times \frac{a}{b} \times \frac{b}{a}=25\)
    \(\Rightarrow \frac{a^{2}}{b^{2}}+\frac{b^{2}}{a^{2}}=25-2\)
    \(\Rightarrow \frac{a^{2}}{b^{2}}+\frac{b^{2}}{a^{2}}=23\)
  • Question 10
    1 / -0

    A two member committee comprising of one male and one female member is to be constitute out of five males and three females. Amongst the females. Ms. A refuses to be a member of the committee in which Mr. B is taken as the member. In how many different ways can the committee be constituted ?

    Solution
    5C1 × 3C1 - 1
    = 15 - 1
    = 14
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