> Solution (i) For odd numbers a=1d=2 last term (less than 50) = 49 an=a+(n−1)d1+(n−1)2=49(n−1)2=48n−1=24n=25 Sum of n terms, Sn=n2[a+l]S25=252[1+49]=252×50=625 (ii) For multiples of 7 a=7d=7n=12 Sum of n terms, Sn=n2[2a+(n−1)d]S12=122[2(7)+11×7]=6×[14+77]=6×91=546 Mathematics Concise Mathematics Standard X
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