Question

[Bùi Quỳnh Anh]

làm 1 trong số đó cũng đc

Answer 1

[Nguyễn Lê Phước Thịnh]

Bài 5:

a: \(A=23-21+19-17+15-13+11-9+7-5+3-1\)

=(23-21)+(19-17)+(15-13)+(11-9)+(7-5)+(3-1)

=2+2+2+2+2+2

=12

b: \(B=24-22+20-18+16-14+12-10+8-6+4-2\)

=(24-22)+(20-18)+(16-14)+(12-10)+(8-6)+(4-2)

=2+2+2+2+2+2

=12

c: \(C=3+5+7+9+11+13+15+17+19\)

=(3+19)+(5+17)+(7+15)+(9+13)+11

=22+22+22+22+11

=99

d: Số số hạng là \(\dfrac{101-3}{2}+1=\dfrac{98}{2}+1=50\left(số\right)\)

Tổng của dãy số là:

\(D=\left(101+3\right)\cdot\dfrac{50}{2}=104\cdot25=2600\)

Bài 4:

1: \(13\cdot58\cdot4+32\cdot26\cdot2+52\cdot10\)

\(=52\cdot58+52\cdot32+52\cdot10\)

\(=52\left(58+32+10\right)=52\cdot100=5200\)

2: \(15\cdot37\cdot4+120\cdot21+21\cdot5\cdot12\)

\(=60\cdot37+60\cdot42+60\cdot21\)

=60(37+42+21)

=60*100=6000

3: \(14\cdot35\cdot5+10\cdot25\cdot7+20\cdot70\)

\(=70\cdot35+70\cdot25+70\cdot20\)

\(=70\left(35+25+20\right)=70\cdot80=5600\)

4: \(15\cdot\left(27+18+6\right)+15\cdot\left(23+12\right)\)

\(=15\cdot\left(45+6+35\right)=15\cdot86=1290\)

5: \(24\cdot\left(15+49\right)+12\cdot\left(50+42\right)\)

\(=24\cdot64+12\cdot92=24\cdot64+24\cdot46=24\cdot\left(64+46\right)\)

\(=24\cdot110=2640\)