b) 7+14+21 +. .+ 140-c) -1+6+ 13+ + 132- – InterviewSolution

1.	b) 7+14+21 +. .+ 140-c) -1+6+ 13+ + 132-
Answer» (a) 1+2+3+....+20=2021/2=210(b) 7+14+21+....+140=7(1+2+3..+20)=72021/2=1470(c)-1+6+13+...132suppose total number of terms are nso 132=-1+(n-1)7133=(n-1)7n-1=19n=20so sum=(20/2)(-1+132)=10131=1310

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