Question

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Answer 1

[{a+(3n-1)d}-{a+(n-1-1)d}]/[{a+(2n-1)d}-{a+(2n-1-1)d}] =31,

[a+3nd-d-a-nd+2d]/[a+2nd-d-a-2nd+2d] =31,

(2nd+d)/(d)=31,

then
2n+1=31,

2n=31-1,

then

2n=30,

n=15