a+2a+3a+...+100a+b+2b+3b+...100b
= (a + b) + 2(a + b) + 3(a + b).+100(a + b)
= 1 + 2 + 3 + .+ 100
= (1 + 100) × (100 ÷ 2)
= 101 × 50
= 5050
a+2a+3a+...+100a+b+2b+3b+...100b
= (a + b) + 2(a + b) + 3(a + b).+100(a + b)
= 1 + 2 + 3 + .+ 100
= (1 + 100) × (100 ÷ 2)
= 101 × 50
= 5050