Tính bằng cách thuận tện
\(\dfrac{13}{60}\) + \(\dfrac{18}{30}\) +\(\dfrac{11}{60}\)
K
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8 tháng 3 2022
\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{5\times4\times13}{13\times5\times3}=\dfrac{4}{3}\\ b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\dfrac{3}{7}\times\dfrac{7}{5}+\dfrac{5}{2}\times\dfrac{7}{5}=\dfrac{3}{5}+\dfrac{7}{2}=\dfrac{6}{10}+\dfrac{35}{10}=\dfrac{41}{10}\\ c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)
1
15 tháng 5 2023
a: =13/26*9/18*2/3=2/3*1/4=2/12=1/6
b: =44/22*5/15*3/2=2*1/3*3/2=2*1/2=1
ND
Nguyễn Đức Trí
VIP
8 tháng 8 2023
\(A=\dfrac{10}{7.12}+\dfrac{10}{12.17}+\dfrac{10}{17.22}+...+\dfrac{10}{502.507}\) (sửa 502+507 thành 503.507)
\(\Rightarrow A=10\left(\dfrac{1}{7.12}+\dfrac{1}{12.17}+\dfrac{1}{17.22}+...+\dfrac{1}{502.507}\right)\)
\(\Rightarrow A=10.\dfrac{1}{5}\left(\dfrac{1}{7}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{17}+\dfrac{1}{17}-\dfrac{1}{22}+...+\dfrac{1}{502}-\dfrac{1}{507}\right)\)
\(\Rightarrow A=2.\left(\dfrac{1}{7}-\dfrac{1}{507}\right)=2.\left(\dfrac{500}{3549}\right)=\dfrac{1000}{3549}\)
\(B=\dfrac{4}{8.13}+\dfrac{4}{13.18}+\dfrac{4}{18.23}+...+\dfrac{4}{253.258}\)
\(\Rightarrow B=4\left(\dfrac{1}{8.13}+\dfrac{1}{13.18}+\dfrac{1}{18.23}+...+\dfrac{1}{253.258}\right)\)
\(\Rightarrow B=4.\dfrac{1}{5}\left(\dfrac{1}{8}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{18}+\dfrac{1}{18}-\dfrac{1}{23}+...+\dfrac{1}{253}-\dfrac{1}{258}\right)\)
\(\Rightarrow B=\dfrac{4}{5}\left(\dfrac{1}{8}-\dfrac{1}{258}\right)=\dfrac{4}{5}\left(\dfrac{129}{1032}-\dfrac{8}{1032}\right)=\dfrac{4}{5}.\dfrac{121}{1032}=\dfrac{121}{1290}\)
12 tháng 11 2022
60x [7/12+4/15]
60x153/180
=9180/180
b 1/2x2/3x3/4x4/5x5/6x6/7x7/8x8/9=40320/4032
NK
2
11 tháng 3 2017
Ta có: \(\dfrac{5}{2}+\dfrac{4}{11}+\dfrac{3}{22}+\dfrac{1}{30}+\dfrac{13}{60}\)
= \(\dfrac{5.11}{2.11}+\dfrac{4.2}{11.2}+\dfrac{3}{22}+\dfrac{1.2}{30.2}+\dfrac{13}{60}\)
= \(\dfrac{55}{22}+\dfrac{8}{22}+\dfrac{3}{22}+\dfrac{2}{60}+\dfrac{13}{60}\)
= \(\dfrac{55+8+3}{22}+\dfrac{2+13}{60}\)
=\(\dfrac{66}{22}+\dfrac{15}{60}\)
= \(3+\dfrac{1}{4}\)
= \(\dfrac{13}{4}\)
\(\dfrac{13}{60}+\dfrac{18}{30}+\dfrac{11}{60}=\dfrac{13+11}{60}+\dfrac{18}{30}\)
\(=\dfrac{24}{60}+\dfrac{36}{60}=\dfrac{60}{60}=1\)
= 13/60 + 36/60 + 11/60
= (13+36+11)/60
= 1