A = 1.2 + 2.3 + 3.4 + ...... + 100.101
3A = 1.2.3 + 2.3.3 + 3.4.3 + ...... + 100.101.3
3A = 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + ..... + 100.101.(102 - 99)
3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ...... + 100.101.102 - 99.100.101
3A = 100.101.102
A = 100.101.34
A = 343400