$\frac{3}{1.4}$ + $\frac{3}{4.7}$ + ... + $\frac{3}{40.43}$
= 1 - $\frac{1}{4}$ + $\frac{1}{4}$ - $\frac{1}{7}$ +... + $\frac{1}{40}$ - $\frac{1}{43}$
= 1 - $\frac{1}{43}$
= $\frac{42}{43}$
Vậy $\frac{3}{1.4}$ + $\frac{3}{4.7}$ + ... + $\frac{3}{40.43}$= $\frac{42}{43}$