Gọi biểu thức đó là A. Ta có:
A=11.4+14.7+17.10+...+167.70
3A = 3.(11.4+14.7+17.10+...+167.70)
3A = 31.4+34.7+37.10+...+367.70
3A = 1−14+14−17+17−110+...+167−170
3A = 1−170
3A = 6970
=> A = 6970:3
A = 6970.13
A = 2370

Gọi biểu thức đó là A. Ta có:
A=\(\dfrac{1}{1.4}+\dfrac{1}{4.7}+\dfrac{1}{7.10}+...+\dfrac{1}{67.70}\)
3A = \(3.\left(\dfrac{1}{1.4}+\dfrac{1}{4.7}+\dfrac{1}{7.10}+...+\dfrac{1}{67.70}\right)\)
3A = \(\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{67.70}\)
3A = \(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{67}-\dfrac{1}{70}\)
3A = \(1-\dfrac{1}{70}\)
3A = \(\dfrac{69}{70}\)
=> A = \(\dfrac{69}{70}:3\)
A = \(\dfrac{69}{70}.\dfrac{1}{3}\)
A = \(\dfrac{23}{70}\)