Question

The sum of first 10 terms in ap is 16 and the last is 60 the sum of the ap is 342 find the comnon difference

Answer 1

let the a.p be a;a+d; a+2d .......a+nd

sum of 10 terms is 10a +(1+2+3+4+5+6+7+8+9)d

i.e 10a + 55d

given 10a +55d =16 .......(1)

and sum of 60a + (n+n-1 +n-2 +n-3 +........+n-59)d

i.e 60a+(60n-(1+2+3+4+......59))d

i.e 60a+ (60n-(59×60)/2)d

i.e60a+(60n-1770)d

60a+(60n-1770)d =342.....(2)

solve (1)&(2) u get the answer