Môn Toán Lớp 6: B=4/10.11 + 4/11.12 + 4/12.13 +….+4/2019.2020

B = 4/{10.11} + 4/{11.12} + 4/{12.13} + … + 4/{2019.2020}

B = 4. ( 1/{10.11} + 1/{11.12} + 1/{12.13} + … + 1/{2019.2020} )

B = 4. ( 1/10 – 1/11 + 1/11 – 1/12 + 1/12 – 1/13 + … + 1/2019 – 1/2020 )

B = 4. ( 1/10 – 1/2020 )

B = 4. 201/2020

B = 201/505