Tính :
A=\(\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+......+\dfrac{1}{120}\)
B=\(\dfrac{4}{3.7}+\dfrac{4}{7.11}+\dfrac{4}{11.15}+......+\dfrac{4}{107.111}\)
C=\(\dfrac{7}{10.11}+\dfrac{7}{11.12}+\dfrac{7}{12.13}+......+\dfrac{7}{69.70}\)
D=\(\dfrac{15}{90.94}+\dfrac{15}{94.98}+\dfrac{15}{98.102}+......+\dfrac{15}{146.150}\)