The sum

The sum of the first 10 members of the arithmetic sequence is 120. What will be the sum if the difference is reduced by 2?

Correct result:

s2 =  30

Solution:

s1=120 n=10  s1=a1+a2+a3++an  d2=d12  s1=10/2 (a1+a1+9 d1)=10 a1+45 d1=120 s2=10/2 [a1+a1+9 (d12)] s2=10 a1+45 d15 9 2  s2=s15 9 2=1205 9 2=30



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