Bài 1:Tính nhanh:
a,6/4*8 +6/8*12 +...+ 6/76*80
b,12/6*12+12/12*18+...+12/54*60
a) Tính bằng hai cách:
(15 +35) : 5;
(80 +4) : 4
b) Tính bằng hai cách (theo mẫu)
Mẫu: 12 : 4 + 20 : 4 = ?
Cách 1:
12 : 4 + 20 : 4
= 3 + 5 = 8
Cách 2:
12 : 4 + 20 : 4
= (12+20) : 4
= 32 :4 = 8
18 : 6 + 24 : 6;
60 : 3 + 9 : 3.
a) (15 +35) : 5 = ?
Cách 1: (15 +35) : 5
= 50 : 5 = 10
Cách 2: (15 +35) : 5
= 15 : 5 + 35 : 5
= 3 + 7 = 10
+) (80 +4) : 4 = ?
Cách 1:(80 +4) : 4
= 84 : 4 = 21
Cách 2:(80 +4) : 4
= 80 : 4 + 4 :4 = 20 +1 = 21
b) 18 : 6 + 24 : 6 = ?
Cách 1: 18 : 6 + 24 : 6
= 3 + 4 = 7
Cách 2: (18 + 24) : 6
= 42 : 6 = 7
+) 60 : 3 + 9 : 3 =?
Cách 1: 60 : 3 + 9 : 3
= 20 + 3 = 23
Cách 2: 60 : 3 + 9 : 3
=(60 +9) : 3 = 23
a) (15 +35) : 5 = ?
Cách 1: (15 +35) : 5
= 50 : 5 = 10
Cách 2: (15 +35) : 5
= 15 : 5 + 35 : 5
= 3 + 7 = 10
+) (80 +4) : 4 = ?
Cách 1:(80 +4) : 4
= 84 : 4 = 21
Cách 2:(80 +4) : 4
= 80 : 4 + 4 :4 = 20 +1 = 21
b) 18 : 6 + 24 : 6 = ?
Cách 1: 18 : 6 + 24 : 6
= 3 + 4 = 7
Cách 2: (18 + 24) : 6
= 42 : 6 = 7
+) 60 : 3 + 9 : 3 =?
Cách 1: 60 : 3 + 9 : 3
= 20 + 3 = 23
Cách 2: 60 : 3 + 9 : 3
=(60 +9) : 3 = 23
HT1.Tính:
a.135 : 5 + 12 x3 : 6 - 17
b.34 :[(80 :4 + 10) : 6 + 12 ] +100
2.tính nhanh:
A= 4+ 8+12 +.....+80
B= 2+4-6+8+10-12+...+62+62-66
1.
A.16
B.102
2.
SSH=( 80-4):4+1=20
TỔNG A= (80+4)*20:2=840
Tính nhẩm
42 : 6 = ..... 48 : 6 = ..... 6 : 6 = ..... 12 : 3 = .....
18 : 6 = ..... 54 : 6 = ..... 30 : 6 = ..... 12 : 4 = .....
24 : 6 = ..... 60 : 6 = ..... 36 : 6 = ..... 12 : 6 = .....
42 : 6 = 7 48 : 6 = 8 6 : 6 = 1 12 : 3 = 4
18 : 6 = 3 54 : 6 = 9 30 : 6 = 5 12 : 4 = 3
Bài 3: Tính nhẩm:
a) 9 . 24 . 25 ;
b) 12 . 125 . 54 ;
c) 64 . 125 . 875 ;
d) 425 . 7 . 4 – 170 . 60 ;
e) 8 . 9 . 14 6 . 17 . 12 19 . 4 . 18.
Trả lời
a) 9 . 24 . 25 = 9 . 600 = 5400
b) 12 . 125 . 54 = 1500 . 54 = 81000
c) 64 . 125 . 875 = 8000 . 875 = 7000000
d) 425 . 7 . 4 - 170 . 60 = 11900 - 10200 = 1700
e) 8 . 9 . 14 . 6 . 17 . 12 . 19 . 4 . 18 =
a) 5400
b) 81000
c) 7000000
d) 1700
e) 15684492672
^.^
a) 9 . 24 . 25 = 3.3.3.4.2.25 = (25.4).(3.3.3.2) = 100.54 = 5 400
b) 12 . 125 . 54 = 4.3.125.2.3.3.3 = (125.2.4).(3.3.3.3) = 1000.81 = 81 000
c) 64 . 125 . 875 = (125.64).875 = 8000.875 = 7 000 000
d) 425 . 7 . 4 – 170 . 60 = 25.17.7.4 - 2.5.17.4.3.5 = 25.17.7.4 - 25.17.6.4 = 25.17.4.(7-6) = (25.4).17 = 100.17 = 1 700
Đề bài câu e sai rồi bn, như này mới đúng:
e) 8 . 9 . 14 + 6 . 17 . 12 + 19 . 4 . 18 = (2.2.2.3.3).2.7 + (2.3.2.2.3).17 + (2.2.2.3.3).19 = 72.14 + 72.17 + 72.19 = 72.(14+17+19)
= 72.50 = 36.2.50 = 36.100 = 3 600
tính nhanh : a, 9 x 12 x25 b, 12 x 125 x 54 c, 8 x 9 x 14 + 6 x 7 x 12 + 19 x 4 x 18 d, 425 x 7 x 4 - 170 x 60 e, 1 + 5 + 9 + 13 + ... + 57 + 61 + 65
a,9.3.4.25
= 27.100
= 2700
b, 12.125.54
= 3.4.125.54
= 125.4.3.54
= 500.162
= 81000
c: \(=72\cdot14+72\cdot7+72\cdot19=72\cdot40=2880\)
d: \(=1700\cdot7-1700\cdot6=1700\)
e: Số số hạng là (65-1)/4+1=17(số)
Tổng là: \(\dfrac{65+1}{2}\cdot17=33\cdot17=561\)
Bài 2: Viết tiếp 2 số hạng vào dãy số sau:
a) 10, 13, 18, 26, ...
b) 0, 1, 2, 4, 7, 12, ...
c) 0, 1, 4, 9, 18, ...
d) 5, 6, 8, 10, ...
e) 1, 6, 54, 648, ... ...
k) 1, 3, 3, 9, 27,
L) 1, 2, 3, 6, 12, 24....
m) 1, 4, 9, 16, 25, 36,
o) 2, 12, 30, 56, 90,
p) 1, 3, 9, 27, ....
g) 1, 5, 14, 33, 72, h) 2, 20, 56, 110, 182.....
q) 2, 6, 12, 20, 30, ...
t) 6, 24, 60, 120, 210...
a) 10; 13; 18; 26; 36; 52...
c) 0; 1; 4; 9; 16; 25...
m) 1; 4; 9; 16; 25; 36; 49; 64...
p) 1; 3; 9; 27; 81; 243...
Tính nhanh: A) 4/9+1/8+5/9+7/8 B) 1/6+4/6+5/12+7/6+7/12
a: \(=\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{1}{8}+\dfrac{7}{8}\right)=1+1=2\)
b: \(=\left(\dfrac{1}{6}+\dfrac{4}{6}+\dfrac{7}{6}\right)+\left(\dfrac{5}{12}+\dfrac{7}{12}\right)=2+1=3\)
Tính nhanh:
a,1/4+2/5+6/8+9/15+8/1
b,1/2+2/4+3/6+4/8+5/10+6/12+7/14+8/16+9/18+10/20
c,1/10+4/20+9/30+16/40+25/50+36/60+49/70+64/80+81/90
a; \(\dfrac{1}{4}\) + \(\dfrac{2}{5}\) + \(\dfrac{6}{8}\) + \(\dfrac{9}{15}\) + \(\dfrac{8}{1}\)
= (\(\dfrac{1}{4}\) + \(\dfrac{6}{8}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{9}{15}\)) + \(\dfrac{8}{1}\)
= (\(\dfrac{1}{4}\) + \(\dfrac{3}{4}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{3}{5}\)) + 8
= 1 + 1 + 8
= 2 + 8
= 10
b; \(\dfrac{1}{2}\) + \(\dfrac{2}{4}\) + \(\dfrac{3}{6}\) + \(\dfrac{4}{8}\) + \(\dfrac{5}{10}\) + \(\dfrac{6}{12}\) + \(\dfrac{7}{14}\) + \(\dfrac{8}{16}\) + \(\dfrac{10}{20}\)
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x (\(\dfrac{2}{2}\) + \(\dfrac{3}{3}\) + \(\dfrac{4}{4}\) + \(\dfrac{5}{5}\)+ \(\dfrac{6}{6}+\dfrac{7}{7}+\dfrac{8}{8}\) + \(\dfrac{10}{10}\))
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x (1 + 1 +1 + 1+ 1+ 1+ 1 +1)
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x 1 x 8
= \(\dfrac{1}{2}\) + \(\)\(\dfrac{1}{2}\) x 8
= \(\dfrac{1}{2}\) + 4
= \(\dfrac{9}{2}\)
Tính nhanh:
a,1/4+2/5+6/8+9/15+8/1
b,1/2+2/4+3/6+4/8+5/10+6/12+7/14+8/16+9/18+10/20
c,1/10+4/20+9/30+16/40+25/50+36/60+49/70+64/80+81/90