11th Class Mathematics Sequence and Series Question Bank Sequence and Series (A.P., G.P. and H.P.)

  • question_answer
    Two APs have the same common difference. The difference between their 100th terms is 100, what is the difference between their 1000th terms?

    A)  100         

    B)  1000             

    C)  1200              

    D)  10000

    Correct Answer: A

    Solution :

    (a): Let the two APs be \[{{a}_{1}},{{a}_{2}},{{a}_{3}},\].......... and\[{{b}_{1}},{{b}_{2}},{{b}_{3}},.....{{b}_{n}}\]. Also, let d be the same common difference of two APs, then The nth term of first AP   \[{{a}_{n}}={{a}_{1}}+(n-1)d\] And the nth term of second AP \[{{b}_{n}}={{b}_{1}}+(n-1)d\] Now, \[{{a}_{n}}-{{b}_{n}}=\left[ {{a}_{1}}+(n-1)d \right]-\left[ {{b}_{1}}+(n-1)d \right]\] \[\Rightarrow {{a}_{n}}-{{b}_{n}}={{a}_{1}}-{{b}_{1}}\forall n\in N\] \[\Rightarrow {{a}_{100}}-{{b}_{100}}={{a}_{1}}-{{b}_{1}}=100\] (Given) \[\therefore \,\,\,{{a}_{1000}}-{{b}_{1000}}={{a}_{1}}-{{b}_{1}}\]                 


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