Given 1st term of the A.P=100=a
And the last term =199=L
Let the three term be a,a+d,a+2d
an=L=a+(n−1)d
di=n−1L−a
n→ number of terms
Now checking for what value of n we have integral common difference,
For, n=3,d1=2199−100
=299∈/I
For, n=4,d2=399=33∈I
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For, n=10,d3=999=11∈I
For, n=12,d4=1199=9∈I
So, sum of all common difference that are integer will be ∑di=33+11+9=53