Question

Find sum of following A.P.:
(a) 8 + 13 + 18 + ……………+ 128

Answer 1

Answer:

8+13+18+23+28+33+38+43+48+53+58+63+68+73+78+83+88+93+98+103+108+113+118+123+128

Step-by-step explanation:

this is because it has a pattern of adding number by 5

Answer 2

Answer:

1700

Step-by-step explanation:

Sₙ=n/2[2a+(n-1)d]

given tₙ=128

    a+(n-1)d=128

     8+(n-1)5=128

        5n+3=128

          n=25

hence S₂₅=25/2[2(8)+(24)5]

                 =25/2[16+120]

                = 25[68]

                     =1700

hope this helps you

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