Question

find the sum of all 2 digit number greater than 50 which when divided by 7 leaves remainder 4...Plz..plz...help me..in last 3 Q.

Answer 1

AP for these numbers is  53,60,...........95,

a = 53
d = 7

Let there are n terms in AP
  so ,an = 95
       a+ (n-1)d = 95
      53+ (n-1)7 = 95
      53-7 + 7n = 95
      46 + 7n = 95
      so, 7n = 95 - 46 
            n = 49/7 = 7

so there are only 7 terms in AP
 
so sum = S7 = 7/2(a+l)
                     = 7/2 (53+95)
                     =7/2 (148)
                     = 7*74
                     = 518

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Answer 2

i hope u will understand. any doubt u will contact me.