PLzzzzz explain!!!!!!!!!!

The common difference of two AP's is same, i.e d = d'

T'₁₀₀ = a'+ (100-1) d'

T₁₀₀ = a + (100-1) d

T'₁₀₀ - T₁₀₀ = 100 = a'+ (100-1) d' - (a + (100-1) d)

                        100  = a' - a                        [Since d =d']

So the difference between their 1000th term is

T'₁₀₀₀ - T₁₀₀₀ = a'+ (1000-1) d' - (a + (1000-1) d) = a' + 999 d'  - a - 999d = a' - a   = 100