Question

B = 10/56 + 10/140+10/260+.....+10/1400    ( phân số nha )
Tính B 

Answer 1

B=5/28+5/70+5/130+...+5/700

B=5/4.7+5/7.10+5/10.13+...+5/25.28

B=5/3.(3/4.7+3/7.10+3/10.13+...+3/25.28)

B=5/3.(1/4-/7+1/7-1/10+1/10+1/10-1/13+...+1/25-1/28)

B=5/3.(1/4-1/28)

B=5/3.3/14

B=5/14

Vậy B=5/14

Answer 2

B=5/3.(3/28+3/70+...+3/700)

B=5/3.(3/4.7+3/7.10+...+3/25.28)

B=5/3.(1/4-1/7+1/7-1/10+...+1/25-1/28)

B=5/3.(1/4-1/28)

B=5/3.3/14

B=5/14

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