a.9phút16giây

b.20phút

còn đặt tinhs thì tự

thích tí mk chụp cho

nếu cần

Bài 2:

6000:30=600:3=200

5462:2=2731

45678:6=7613

Bài 1:

\(36\cdot50=36\cdot5\cdot10=180\cdot10=1800\)

\(59\cdot60=59\cdot6\cdot10=354\cdot10=3540\)

\(90\cdot40=90\cdot4\cdot10=360\cdot10=3600\)

K/c mỗi số là 3 đơn vị.

Tổng đó có số số hạng là:`(40-1):3+1=14`(số)

`=>1+4+7+...+40=((40+1).14)/2=41.7=287`

\(A=\)\(1+4+7+10+...+34+37+40\)

\(A=\)\(40+37+34+31+...+7+4+1\)

\(2A=\)\(41+41+41+41+...+41+41+\text{41}\)

\(2A=41.14=>A=\dfrac{41.14}{2}=287\)

(40-1):\(\)3+1=14 nên ta sẽ có số số hạng là:

(40+1)\(\times\)14:2=287

Chúc bạn học tốt.

Bài 40 :

\(a,\left(\dfrac{3}{7}+\dfrac{1}{2}\right)^2=\left(\dfrac{13}{14}\right)^2=\dfrac{13^2}{14^2}=\dfrac{169}{196}\)

\(b,\left(\dfrac{3}{4}-\dfrac{5}{6}\right)^2=\left(\dfrac{-1}{12}\right)^2=\dfrac{\left(-1\right)^2}{12^2}=\dfrac{1}{144}\)

\(c,\dfrac{5^4.20^4}{25^5.4^5}=\dfrac{5^4.\left(5.4\right)^4}{\left(5^2\right)^5.4^5}=\dfrac{5^4.5^4.4^4}{5^{10}.4^5}=\dfrac{5^8.4^4}{5^{10}.4^5}=\dfrac{1}{5^2.4}=\dfrac{1}{100}\)

\(d,\left(\dfrac{-10}{3}\right)^5.\left(\dfrac{-6}{5}\right)^4=\left(\dfrac{-10}{3}\right)^4.\left(\dfrac{-10}{3}\right).\left(\dfrac{-6}{5}\right)^4=\left(\dfrac{-10}{3}.\dfrac{-6}{5}\right)^4.\left(\dfrac{-10}{3}\right)=4^4.\dfrac{-10}{3}=256.\dfrac{-10}{3}=\dfrac{-2560}{3}\)

Bài 41 :

\(a,\left(1+\dfrac{2}{3}-\dfrac{1}{4}\right).\left(\dfrac{4}{5}-\dfrac{3}{4}\right)^2=\left(\dfrac{12}{12}+\dfrac{8}{12}-\dfrac{3}{12}\right).\left(\dfrac{16}{20}-\dfrac{15}{20}\right)^2=\dfrac{17}{12}.\left(\dfrac{1}{20}\right)^2=\dfrac{17}{12}.\dfrac{1}{400}=\dfrac{17}{4800}\)

\(b,2:\left(\dfrac{1}{2}-\dfrac{2}{3}\right)^3=2:\left(\dfrac{-1}{6}\right)^3=2:\dfrac{-1}{216}=-432\)

10+10=20

20+20=40

30+30=60

40+40=80

tk mk

10+10=20

20+20=40

30+30=60

40=40=80

10 + 10 = 20

20 + 20 = 40 

30 + 30 = 60 

40 + 40 = 80

Cho hỏi trang mấy

giúp mình với

1, C.

2, B.

3, KO CÓ.

4, A.

5, D.

6, C.