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General Test - 26

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  • Question 1
    4 / -1

    A train covers a distance of 20 km in 15 minutes. If its speed is increased by 10 km/hr, the time taken by it to cover the same distance will be:

    Solution

    Distance = 20km

    Time = 15 minutes = 14 hr

    ∴ Speed of the train =DistanceTime

    = 2014 = 80 km/h

    After increasing its speed by 10 km/hr,

    New speed = 90 km/hr

    Distance = 20 km (given)

    ∴ Time = DistanceSpeed

    ∴ Time = 2090 = 29th of an hour = 60 × 29

    Thus, the time taken by the train will be 13 minutes and 20 seconds.

  • Question 2
    4 / -1

    The speed of Ram and Shaym are in the ratio 7 ∶ 8. They both cover a certain distance but Ram takes 45 minutes more than Shyam. Find the time taken by Ram to cover the distance?

    Solution

    Given:

    The speed of Ram and Shaym are in the ratio 7 ∶ 8.

    Ram takes 45 minutes more than Shyam to cover the certain distance.

    Speed =DistanceTime

    Time =DistanceSpeed

    Let the distance be D.

    Let the speed of Ram be 7x and the speed of Shaym be 8x.

    Let Ram takes t1 time to cover the distance and Shyam takes t2 time to cover the distance.

    Time taken by Ram = t1 =D7x

    Time taken by Shyam = t2 =D8x

    Now, Ram takes 45 min more than Shyam.

    ∴ t1 – t2 =D7xD8x=4560

    ⇒ D = 42x

    Now, Time taken by Ram =42x7x = 6 hours.

    ∴ Ram will take 6 hours to cover the dame distance.

  • Question 3
    4 / -1

    Two trains of lengths 160 m and 200 m travel at speeds of 48 m/sec and 52 m/sec respectively in opposite directions to each other. What is the total time taken by them to cross each other?

    Solution

    Relative speed \(=48+52=100 \) m/sec

    Total distance covered by both the trains \(=160+200=360 \) m

    Speed \(=\frac{\text { Distance }}{\text { Time }}\)

    \(\therefore 100=\frac{360}{\text { Time }}\)

    \(\therefore\) Time \(=3.6\) sec

  • Question 4
    4 / -1

    If the roots of \(ax^2+ bx + c =0\) are in the ratio \(m : n\), then:

    Solution

    We have\(\frac{\alpha}{\beta}=\frac{m}{n}\)

    \(\Rightarrow \frac{\alpha}{m}=\frac{\beta}{n}\)

    \( \Rightarrow \frac{\alpha+\beta}{m+n}=\sqrt{\frac{\alpha \beta}{m n}}\) by ratio proportion

    \(\therefore m n(\alpha+\beta)^{2}=\alpha \beta(m+n)^{2}\)

    \(\Rightarrow m n\left(\frac{-b}{a}\right)^{2}=(m+n)^{2} \frac{c}{a}\)

    \(\therefore m n b^{2}=(m+n)^{2} a c\)

  • Question 5
    4 / -1

    If \(24\) is \(\frac{2}{3}\) of \(\frac{3}{4}\) of a number, then what will be \(\frac{1}{4}\) of that number?

    Solution
    Let the number be \(x\).
    Accordimng to the question,
    \(\frac{2}{3} \times \frac{3}{4} \times x=24\)
    \(\Rightarrow \frac{1}{2} \times x=24\)
    \(\Rightarrow x=48\)
    So,\(\frac{1}{4}\) of that number \(=\frac{1}{4} \times 48=12\)
  • Question 6
    4 / -1

    A man bought \(13\) articles at Rs. \(70\) each,\(15\) at Rs.\(60\) each and\(12\) at Rs.\(65\) each. The average price per article is:

    Solution

    Cost of \(13\) articles \(=13 \times 70=\) Rs. \(910\)

    Cost of \(15\) articles \(=15 \times 60=\) Rs. \(900\)

    Cost of \(12\) articles \(12 \times 65=780\)

    Average of each article \(= \frac{910+900+780}{40}= \frac{2590}{40}=\) Rs. \(64.75\)

  • Question 7
    4 / -1

    What is not the value of 5 \(\div\) ( -1) between?

    Solution

     5 \(\div\) ( -1) = -5

    It is placed on the number line asNCERT Exemplar Class 7 Maths Integers Img 7

    Now, as we can see, -5 lies between (0 and -10), (-4 and -15) and (-6 and 6). But it does not lie between 0 and 10.

  • Question 8
    4 / -1

    A vessel of 80 litres is filled with milk and water. 70% of milk and 30% of water is taken out of the vessel. It is found that the vessel is vacated by 55%. Find the initial quantity of milk and water.

    Solution

    Let the initial quantity of milk be x L

    Since The total mixture is 80 L so the initial quantity of water be (80 - x) L

    ⇒ 70% of x + 30% of (80 - x) = 55% of 80⇒0.7x + 0.3 × (80 - x) = 0.55 × 80

    ⇒ x = 50

    Therefore, Initial quantity of milk = 50 L and the initial quantity of water = 30 L

  • Question 9
    4 / -1

    Two letters are chosen randomly from English alphabet. What is the probability that none of them is a vowel and they are consecutive letters?

    Solution

    Any two letters can be chosen in \(=\frac{(26 \times 25)}{2}=325\) ways

    If they are consecutive, they can be \(A B, B C, C D, \ldots Y Z\), a total of \(25\) cases

    Out of these, \(AB, DE, EF, HI, IJ, NO, OP, TU\) and \(UV\) will have vowels

    \(\therefore\) Required probability \(=\frac{(25-9)}{325}=\frac{16}{325}\)

  • Question 10
    4 / -1

    The sides of a triangle are \(m, n\) and \(\sqrt{m^{2}+n^{2}+m n}\). What is the sum of the acute angles of the triangle?

    Solution

    Let \(m=n=1\) unit

    Then \(\sqrt{ m ^{2}+ n ^{2}+ mn }=\sqrt{3}\) unit

    Using cosine rule;

    \(\cos\theta=\frac{a^{2}+b^{2}-c^{2}}{2ab}\)

    After putting the value,

    \(\cos \theta=\frac{1^{2}+1^{2}-\sqrt{3}^{2}}{2 \times 1 \times 1}\)

    \(\Rightarrow \cos\theta=\frac{1+1-3}{2\times1\times1}\)

    \(\Rightarrow \cos \theta=-\frac{1} {2}\)

    \(\therefore \theta=120^{\circ}\)   \(\left[\because \cos 120^{\circ}=-\frac{1}{2}\right]\)

    Now, the sum of the acute angles of the triangle \(=180^{\circ}-120^{\circ}\)

    \(=60^{\circ}\)

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