Question

find the sums of all multiples of 9 lying between 400 and 900?

fast please urgent required​

Answer 1

Answer:

The first multiple of 9 between 400 and 800 is 405 and the last multiple is 792.

We know that An = a+(n-1)*d

                        792 = 405(n-1) * 9

                        387 = (n-1) * 9

                           n = 44.

Sum = n/2 * (2a+(n-1)*d)

       = 44/2(2 * 405 + (44-1) * 9)

      = 22(810 + 387)

     = 22 * 1197

     = 26334.

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