10/15 - 2/5 = 10/15 - 6/15 = 4/15

10/15-2/5=10/15-6/15=4/15

\(\dfrac{10}{15}-\dfrac{2}{5}\)

\(=\dfrac{10}{15}-\dfrac{6}{15}\)

\(=\dfrac{4}{15}\)

5/8+4/9

=45/72+32/72

=77/72

\(\dfrac{5}{8}+\dfrac{4}{9}=\dfrac{45}{72}+\dfrac{32}{72}=\dfrac{77}{72}\)

77/72

\(\dfrac{9}{5}\times\dfrac{20}{27}=\dfrac{180}{135}\)

Tử nhân tử, mẫu nhân mẫu

\(\dfrac{9}{5}x\dfrac{20}{27}=\dfrac{220}{15}\)

95×2027=18013595×2027=180135

Tử nhân tử, mẫu nhân mẫu

\(\dfrac{7}{16}+\dfrac{5}{8}x\dfrac{4}{10}=\dfrac{7}{16}+\dfrac{1}{4}=\dfrac{11}{16}\)

7/16 + 5/8 x 4/10

= 7/16 + 1/2

= 30/32

7/16 + 5/8 x 4/10

= 7/16 + 1/2

= 30/32

= 2/3 x 1/5 

= 2/15

2/15

2/15

\(x=\dfrac{4}{7}:\dfrac{3}{5}=\dfrac{4\times5}{7\times3}=\dfrac{20}{21}\)

=>x=4/7:3/5

x=4/7 x 5/3

x=20/21

\(\dfrac{3}{5}\times x=\dfrac{4}{7}\\ x=\dfrac{4}{7}:\dfrac{3}{5}\\ x=\dfrac{4}{7}\times\dfrac{5}{3}\\ x=\dfrac{20}{21}\)

( 7/4+5/4) x 5/3= 12/4 x 5/3 = 3 x 5/3= 5

5

5

\(=\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=1+1=2\)

2

= 2

A = 5 + 5² + ....+ 5¹⁰⁰

A = 5.( 1 + 5 + ...+ 5⁹⁹)

A > 5 mà A ⋮ 1; 5; A vậy A là hợp số