1. Starting salary = a = Rs 5000 annual increment (common difference) = d = Rs 200 Let, after n years, his salary become Rs 7000. Therefore, a_n = 7000 ⇒ a + (n -1)d = 7000 ⇒ 5000 + (n - 1)(200) = 7000 ⇒ (n -1)(200) = 2000 ⇒ n - 1 = 10 ⇒ n = 11 Hence, in 11th year his salary become Rs 7000.

    Starting salary = a = Rs 5000 annual increment (common difference) = d = Rs 200
    Let, after n years, his salary become Rs 7000.
    Therefore, a_n = 7000
    ⇒ a + (n -1)d = 7000
    ⇒ 5000 + (n – 1)(200) = 7000
    ⇒ (n -1)(200) = 2000
    ⇒ n – 1 = 10 ⇒ n = 11
    Hence, in 11th year his salary become Rs 7000.

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  2. The 20th term from the last term of an AP: 3, 8, 13, ... 253 = the 20th term from the beginning of the AP: 253. 13, 8, 3. In the A.P.: 253, ..., 13, 8, 3, first term = 253 and common difference = 3 - 8 = -5 Therefore, a_20 = a + 19d ⇒ a_20 = 253 + 19(-5) = 253 - 95 = 158

    The 20th term from the last term of an AP: 3, 8, 13, … 253 = the 20th term from the beginning of the AP: 253. 13, 8, 3.
    In the A.P.: 253, …, 13, 8, 3, first term = 253 and common difference = 3 – 8 = -5
    Therefore, a_20 = a + 19d
    ⇒ a_20 = 253 + 19(-5) = 253 – 95 = 158

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  3. First term = 3 and common difference = 15 - 3 = 12 Let the nth term of AP: 3, 15, 27, 39 ... will be 132 more than its 54th term. Therefore, a_n = a₅₄ + 132 ⇒ a + (n -1)d = a + 53d + 132 ⇒ (n -1)(12) = 53 × 12 + 132 ⇒ (n -1)(12) = 768 ⇒ n -1 = 768/12 = 64 ⇒ n = 65 Hence, 65th term of the AP: 3, 15,Read more

    First term = 3 and common difference = 15 – 3 = 12
    Let the nth term of AP: 3, 15, 27, 39 … will be 132 more than its 54th term.
    Therefore, a_n = a₅₄ + 132
    ⇒ a + (n -1)d = a + 53d + 132
    ⇒ (n -1)(12) = 53 × 12 + 132
    ⇒ (n -1)(12) = 768
    ⇒ n -1 = 768/12 = 64
    ⇒ n = 65
    Hence, 65th term of the AP: 3, 15, 27, 39 . . . will be 132 more than its 54th trem.

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  4. Let the first term = a and common difference = d According to question, a₁₇ = a_10 + 7 ⇒ a + 16d = a + 9d + 7 ⇒ 7d = 7 ⇒ d = 1 Hence, the common difference is 1.

    Let the first term = a and common difference = d
    According to question, a₁₇ = a_10 + 7
    ⇒ a + 16d = a + 9d + 7
    ⇒ 7d = 7 ⇒ d = 1
    Hence, the common difference is 1.

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  5. Here, a₃ = 4 and a₉ = - 8. To find : n, where a_n = 0 Given that: a₃ = a + (3 - 1)d = 4 ⇒ a + 2d = 4 ⇒ a = 4 - 2d . . .(1) and a₉ = - 8 ⇒ a + 8d = - 8 Putting the value of a from equation (1), we get 4 - 2d + 8d = -8 ⇒ 6d = - 12 ⇒ d = -2 putting the value of d in equation (1), we get a = 4 - 2(- 2)Read more

    Here, a₃ = 4 and a₉ = – 8. To find : n, where a_n = 0
    Given that: a₃ = a + (3 – 1)d = 4
    ⇒ a + 2d = 4
    ⇒ a = 4 – 2d . . .(1)
    and a₉ = – 8
    ⇒ a + 8d = – 8
    Putting the value of a from equation (1), we get
    4 – 2d + 8d = -8
    ⇒ 6d = – 12 ⇒ d = -2
    putting the value of d in equation (1), we get
    a = 4 – 2(- 2) = 8
    putting the values in a_n = 0, we get
    a_n = a + (n -1)d = 0
    ⇒ 8 +(n -1)(- 2) = 0
    ⇒ n – 1 = 1 = 4 ⇒ n = 5
    Hence, the 5th term of this AP is zero.

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