B = \(\dfrac{5}{2.6}\)+ \(\dfrac{5}{6.10}\)+...+\(\dfrac{5}{402.406}\)
B = 5.( \(\dfrac{1}{2.6}\)+ \(\dfrac{1}{6.10}\)+...+\(\dfrac{1}{402.406}\))
B = 5.(\(\dfrac{1}{2}\) - \(\dfrac{1}{6}\)+ \(\dfrac{1}{6}\)- \(\dfrac{1}{10}\)+...+\(\dfrac{1}{402}\)-\(\dfrac{1}{406}\))
B = 5.(\(\dfrac{1}{2}\) - \(\dfrac{1}{406}\))
B = 5.\(\dfrac{101}{203}\)
B = \(\dfrac{505}{203}\)