câu 3:C
câu 4:A
câu 5:D
câu 6:C
câu 7:A
câu 8:A
tự luận
câu9:
a)\(\dfrac{9}{13}+\dfrac{5}{13}\)
\(=\dfrac{14}{13}\)
b)\(\dfrac{4}{9}.\dfrac{2}{6}\)
\(=\dfrac{4}{27}\)
c)\(1\dfrac{1}{3}.\left(0.5\right)+\left(\dfrac{8}{15}-\dfrac{19}{30}\right):\dfrac{6}{15}\)
\(=\dfrac{4}{3}.\dfrac{-1}{2}+\left(\dfrac{8}{15}-\dfrac{19}{30}\right):\dfrac{6}{15}\)
\(=\dfrac{4}{3}.\dfrac{-1}{2}+\dfrac{-1}{10}:\dfrac{6}{15}\)
\(=\dfrac{-2}{3}+\dfrac{-1}{4}\)
\(=\dfrac{-11}{12}\)
câu 10:
a)x-10=12
x=12+10
x=22
vậy x=22
b)\(x.\dfrac{3}{4}=\dfrac{1}{6}\)
\(x=\dfrac{1}{6}:\dfrac{3}{4}\)
\(x=\dfrac{2}{9}\)
c)\(\left(\dfrac{2}{7}.x+\dfrac{3}{7}\right):2\dfrac{1}{5}-\dfrac{3}{7}=1\)
\(\left(\dfrac{2}{7}.x+\dfrac{3}{7}\right):\dfrac{11}{5}-\dfrac{3}{7}=1\)
\(\left(\dfrac{2}{7}.x-\dfrac{3}{7}\right):\dfrac{11}{5}=1+\dfrac{3}{7}\)
\(\left(\dfrac{2}{7}.x-\dfrac{3}{7}\right):\dfrac{11}{5}=\dfrac{10}{7}\)
\(\dfrac{2}{7}.x-\dfrac{3}{7}=\dfrac{10}{7}.\dfrac{11}{5}\)
\(\dfrac{2}{7}.x-\dfrac{3}{7}=\dfrac{22}{7}\)
\(\dfrac{2}{7}.x=\dfrac{22}{7}+\dfrac{3}{7}\)
\(\dfrac{2}{7}.x=\dfrac{25}{7}\)
\(x=\dfrac{25}{7}:\dfrac{2}{7}\)
\(x=\dfrac{25}{2}\)
vậy \(x=\dfrac{25}{2}\)
câu 11:số học sinh trung bình của lớp 6a chiếm số phần trăm là:
3:4.100%=75%
số học khá của lớp 6a chiếm số phần trăm là:
100%-6,25%-75%=18,75%
câu 13
\(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+\dfrac{1}{5^2}+...+\dfrac{1}{100^2}< 1\)
vì \(\dfrac{1}{2^2}< \dfrac{1}{1.2}\)
\(\dfrac{1}{3^2}< \dfrac{1}{2.3}\)
\(\dfrac{1}{4^2}< \dfrac{1}{3.4}\)
\(\dfrac{1}{5^2}< \dfrac{1}{4.5}\)
...
\(\dfrac{1}{100^2}< \dfrac{1}{99.100}\)
=>P<\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{99.100}\)
P<\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{99}-\dfrac{1}{100}\)
P<\(1-\dfrac{1}{100}\)
P<\(\dfrac{99}{100}\)
vì\(\dfrac{99}{100}< 1\)
=> P<1
vậy P<1
Làm câu 7 tự luận nhé
