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Find the i. 10th term of 3, 7, 11, 15,... ii. 15th term of 10, 7, 4, 1,... iii. 20th term of 5, 10, 15, 20,...

Mathematics

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Answers

3 parts
i

39\text{39}

ii

-32\text{-32}

iii

100\text{100}

Step-by-step solution

9 steps

These are arithmetic progressions. The formula for the nthn^{th} term of an arithmetic progression is Tn=a+(n−1)dT_n = a + (n-1)d, where aa is the first term and dd is the common difference.

Part i· 3 steps

Find the 10th10^{th} term of 3,7,11,15,…3, 7, 11, 15, \dots

  1. Identify the first term (aa) and the common difference (dd).

    The first term is a=3a = 3.
    The common difference is d=7−3=4d = 7 - 3 = 4.

  2. Use the formula for the nthn^{th} term with n=10n=10.

    T10=a+(10−1)dT_{10} = a + (10-1)d T10=3+(9)(4)T_{10} = 3 + (9)(4)
  3. Calculate the 10th10^{th} term.

    T10=3+36T_{10} = 3 + 36 T10=39T_{10} = 39

    The 10th10^{th} term is 39\boxed{\text{39}}.

Part ii

-32\text{-32}

Find the 15th15^{th} term of 10,7,4,1,…10, 7, 4, 1, \dots

  1. Identify the first term (aa) and the common difference (dd).

    The first term is a=10a = 10.
    The common difference is d=7−10=−3d = 7 - 10 = -3.

  2. Use the formula for the nthn^{th} term with n=15n=15.

    T15=a+(15−1)dT_{15} = a + (15-1)d T15=10+(14)(−3)T_{15} = 10 + (14)(-3)
  3. Calculate the 15th15^{th} term.

    T15=10−42T_{15} = 10 - 42 T15=−32T_{15} = -32

    The 15th15^{th} term is -32\boxed{\text{-32}}.

Part iii

100\text{100}

Find the 20th20^{th} term of 5,10,15,20,…5, 10, 15, 20, \dots

  1. Identify the first term (aa) and the common difference (dd).

    The first term is a=5a = 5.
    The common difference is d=10−5=5d = 10 - 5 = 5.

  2. Use the formula for the nthn^{th} term with n=20n=20.

    T20=a+(20−1)dT_{20} = a + (20-1)d T20=5+(19)(5)T_{20} = 5 + (19)(5)
  3. Calculate the 20th20^{th} term.

    T20=5+95T_{20} = 5 + 95 T20=100T_{20} = 100

    The 20th20^{th} term is 100\boxed{\text{100}}.

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