A=5/20+5/30+5/42+...+5/240
A=5/4.5+5/5.6+5/6.7+...+5/15.16
A=5.(1/4.5+1/5.6+1/6.7+...+1/15.16)
A=5.(1/4-1/5+1/5-1/6+1/6-1/7+...+1/15-1/16)
A=5.(1/4-1/16)
A=5.3/16
A=15/16
Vậy A=15/16
A=5/20 + 5/30 + 5/42 +...+5/240
Tính nhanh:
a) 5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90
b) Tính tổng của 10 phân số trong phép cộng sau:
1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/7289/90
Bài 5: Tính nhanh tổng sau(nếu có):
M=\(\dfrac{3}{2}\)-\(\dfrac{5}{6}\)+\(\dfrac{7}{12}\)-\(\dfrac{9}{20}\)+\(\dfrac{11}{30}\)-\(\dfrac{13}{42}\)+\(\dfrac{15}{56}\)-\(\dfrac{17}{72}\) ; A=\(\dfrac{5}{1.3}\)+\(\dfrac{5}{3.5}\)+\(\dfrac{5}{5.7}\)+.....+\(\dfrac{5}{2019.2021}\)
Tính tổng A= 1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+1/90
1, tính tổng
A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72
Tính tổng
A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90
Tính tổng A= 1- 5/6 +7/12 - 9/20 + 11/30 - 13/42 + 15/56 - 17/72 + 19/90 - 21/110 + 23/132 - 25/156
tính nhanh tổng sau ; M=3/2-5/6+7/12-9/20+11/30-13/42+15/56-17/72
a) 15 : (x + 2) = 3 b) 20 : (1 + x) = 2
c) 240 : (x – 5) = 22.52 – 20 d) 96 - 3(x + 1) = 42
