Sequences and Series


  1. Given that 1² + 2² + 3² + ... + 20² = 2870, the value of (2² + 4² + 6² + ..... + 40²) is :









  1. View Hint View Answer Discuss in Forum

    From the question ,
    2² + 4² + 6² + .... + 40² = 2² (1² + 2² + 3² +.... + 20²)

    Correct Option: A

    From the question ,
    2² + 4² + 6² + .... + 40² = 2² (1² + 2² + 3² +.... + 20²)
    Required answer = 4 × 2870 = 11480


  1. Given 1³ + 2³ + 3³ + ... + 10³ = 3025 then 2³ + 4³ + 6³ + ...+ 20³ is equal to









  1. View Hint View Answer Discuss in Forum

    It is given, 1³ + 2³ + 3³ + ... + 10³ = 3025 ........( 1 )
    Now, 2³ + 4³ + 6³ + ... + 20³ = (1 × 2)³ + (2 × 2)³ + (2 × 3)³ + ... + (2 × 10)³
    2³ + 4³ + 6³ + ... + 20³ = 2³ [1³ + 2³ + 3³ + ... + 10³]

    Correct Option: D

    It is given, 1³ + 2³ + 3³ + ... + 10³ = 3025 ........( 1 )
    Now, 2³ + 4³ + 6³ + ... + 20³ = (1 × 2)³ + (2 × 2)³ + (2 × 3)³ + ... + (2 × 10)³
    2³ + 4³ + 6³ + ... + 20³ = 2³ [1³ + 2³ + 3³ + ... + 10³]
    Using the value of equation ( 1 ) , we get
    ∴ 2³ + 4³ + 6³ + ... + 20³ = 8 × 3025 = 24200



  1. 4, 2, 3.5, 7.5, 26.25, 118.125









  1. View Hint View Answer Discuss in Forum

    Series pattern 4 x 0.5 = 2
    2 x 1.5 = 3
    Should come in place of 3.5
    3 x 2.5 = 7.5

    Correct Option: C

    Series pattern 4 x 0.5 = 2
    2 x 1.5 = 3
    Should come in place of 3.5
    3 x 2.5 = 7.5
    7.5 x 3.5 = 26.25
    26.25 x 4.5 = 118.125
    Clearly, 3.5 is wrong and is replaced by 3.


  1. If p, q, r, s are in harmonic progression and p > s, then —









  1. View Hint View Answer Discuss in Forum

    According to question,
    If p, q, r, s are in HP.

    1
    ,
    1
    ,
    1
    ,
    1
    are in AP.
    pqrs

    1
    -
    1
    =
    1
    -
    1
    qpsr

    Correct Option: D

    According to question,
    If p, q, r, s are in HP.

    1
    ,
    1
    ,
    1
    ,
    1
    are in AP.
    pqrs

    1
    -
    1
    =
    1
    -
    1
    qpsr

    1
    +
    1
    =
    1
    +
    1
    qrsp

    Hence, the none of these be answer



  1. What is the eighth term of the sequence 1, 4, 9, 16, 25 ..... ?









  1. View Hint View Answer Discuss in Forum

    According to question,
    1 = (1)²
    4 = (2)²
    9 = (3)²
    16 = (4)²
    25 = (5)²
    Each term of the progression is the square of a natural number.

    Correct Option: B

    According to question,
    1 = (1)²
    4 = (2)²
    9 = (3)²
    16 = (4)²
    25 = (5)²
    Each term of the progression is the square of a natural number. Hence, the eighth term of the sequence will be (8)² = 64