A = 1.2 + 2.3 + 3.4 + ... + 98.99
3A = 1.2.3 + 2.3.3 + 3.4.3 + ...+ 98.99.3
3A = 1.2.3 + 2.3.(4 -1) + 3.4.(5 - 2) + ...+ 98.99.(100 - 97)
3A = (1.2.3 + 2.3.4 + 3.4.5 + ... + 98.99.100) - (0.1.2 + 1.2.3 + 2.3.4 + ... + 97.98.99)
3A = 1.2.3 + 2.3.4 + 3.4.5 + ... + 98.99.100
3A = 98.99.100
=> A = \(\frac{98.99.100}{3}=323400\)