HKIMO 2020 Grade 6 National Final (Heat) Set 01 Question 9

Find $\frac 1{28}+\frac 1{70}+\frac 1{130}+\cdots+\frac 1{418}+\frac 1{550}$. Write the answer in simplest form.

Source glossary (English–Vietnamese): Value: giá trị; Simplest form: dạng tối giản.