\(\dfrac{3}{1.3}+\dfrac{3}{1.5}+...+\dfrac{3}{97.99}\)

\(=\dfrac{3}{2}.\left(\dfrac{1}{1.3}+\dfrac{1}{3.5}+\dfrac{1}{3.7}+...+\dfrac{1}{97.99}\right)\)

\(=\dfrac{3}{2}.\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)\)

\(=\dfrac{3}{2}.\left(1-\dfrac{1}{99}\right)\)

\(=\dfrac{3}{2}.\dfrac{98}{99}\)

\(=\dfrac{1}{1}.\dfrac{49}{33}\)

\(=\dfrac{49}{33}\)

= 1 - 1/3 + 1/ 3 - 1/5 + 1/ 5 - ... + 1/97 -1/99

=1-1/99

=98/99

1 + 1 = 2

2 đó bn

k: \(\dfrac{3}{4}+\dfrac{1}{4}\cdot\left(1,25-\dfrac{3}{4}\right)\cdot\dfrac{5}{8}\)

\(=\dfrac{3}{4}+\dfrac{1}{4}\cdot\dfrac{1}{2}\cdot\dfrac{5}{8}\)

\(=\dfrac{3}{4}+\dfrac{5}{64}=\dfrac{48}{64}+\dfrac{5}{64}=\dfrac{53}{64}\)

m: \(25\%-1\dfrac{1}{2}+0,5\cdot\dfrac{12}{5}\)

\(=0,25-1,5+1,2\)

=-1,25+1,2

=-0,05

n: \(6\dfrac{9}{10}+\left(\dfrac{2}{5}-\dfrac{1}{10}\right)\cdot50\%\)

\(=6,9+0,5\cdot\left(0,4-0,1\right)\)

\(=6,9+0,5\cdot0,3=6,9+0,15=7,05\)

                                             Giải

a] A= SSH [1000 -1] .1 +1 = 1000 [số số hạng]

Tổng [1000 +1].1000 chia 2 = 500500

B= 1.2.3...10.11 = 39916800

Vì 500500 nhỏ hơn 39916800

Nên A bé hơn B

\(1,25\text{ x }x+8,75\text{ x }x=50\\ \left(1,25+8,75\right)\text{ x }x=50\\ 10\text{ x }x=50\\ x=50:10\\ x=5\)

\(1,25\times x+8,75\times x=50\)

\(x\times\left(1,25+8,75\right)=50\)

\(x\times10=50\)

\(x=50:10\)

\(x=5\)

8 giờ kém 5 phút=7h55p

Thời gian ô tô đi hết quãng đường là:

10h30p-7h55p-20p=10h30p-8h15p=2h15p=2,25(giờ)

Độ dài quãng đường từ Hà Nội đến Ninh Bình là:

2,25x48=108(km)

108 km 

bang:1200000

1000x30:2x80

=30000:2x80

=15000x80

=1200000

Phân số lớn là \(\left(\dfrac{13}{12}+\dfrac{1}{4}\right):2=\left(\dfrac{13}{12}+\dfrac{3}{12}\right):2=\dfrac{16}{12}:2=\dfrac{16}{24}=\dfrac{2}{3}\)

Phân số bé là \(\dfrac{2}{3}-\dfrac{1}{4}=\dfrac{8}{12}-\dfrac{3}{12}=\dfrac{5}{12}\)

Cần gấp lắm ạaaaaa 🥹💞🍫