6. tính thuận tiện c) ( A + 9) + ( A- 8) + (A + 7 ) + ( A - 6)+(A + 5) + (A + 44) = 63,3
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a) 8 × 5 × 9 = (8 × 5) × 9 = 40 × 9 = 360
b) 6 × 7 × 5 = (6 × 5) × 7= 30 × 7= 210
c) 6 × 4 × 25 = 6 × (4 × 25) = 6 × 100= 600
a)1+2+3+4+5+6+7+8+9
=(1+9)+(2+8)+(3+7)+(4+6)+5
=10+10+10+10+5
=10x4+5=45
b)8x3+8x7
=8x(3+7)
=8x10=80
c)8x172-8x72
=8x(172-72)
=8x100=800
a. 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 +9
= (1 + 9) + (2 + 8) + (3 + 7) + ( 4 + 6) + 5
= 10 + 10 + 10 + 10 + 5
= 45
=A x (16-9-7): (2+4+6+8+...+20)
=(A x 0): (2+4+6+8+...+20)
=0 x (2+4+6+8+...+20)
=0
a, 23/4 : 3 + 9/4 x 1/3 - 3/8
= 7,8 + 12,22 - 3,8
= 20,02 - 3,8
=16,22
b, 3/5 : 5/6 : 6/7 : 7/8 + 2/5 +23/35
=3/5 x 6/5 x 7/6 x 8/7 + 2/5 + 23/35
=24/25 + 2/5 + 23/35
=1/5 x(24/5 + 2 +23/7)
=1/5 x 353/35
=353/175
a) 13 + 87 : 100
= (13 + 87) : 100
= 100 : 100
= 1
b) 30 + 12 + 70 + 88
= (30 + 70) + (12 + 88)
= 100 + 100
= 200
c) 55 + 44 + 45
= (55 + 45) + 44
= 100 + 44
= 144
c) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10
= (1 + 9) + (2 + 8) + (3 + 7) + (4 + 6) + 5
= 10 + 10 + 10 + 10 + 5
= 40 + 5
= 45
a ) 1
b ) 30 + 12 + 70 + 88
= ( 30 + 70 ) + ( 88 + 13 )
= 100 + 100
= 200
c ) 55 + 44 + 45
= ( 55 + 45 ) + 44
= 100 + 44
= 144
d ) 1+2+3+4+5+6+7+8+9
= ( 1+9 ) + ( 2+8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 5
= 10 + 10 + 10 + 10 + 5
= 45
a) \(2,8+4,7+7,2+5,3\)
\(=\left(2,8+7,2\right)+\left(4,7+5,3\right)\)
\(=10+10=20\)
b) \(12,34+23,87+7,66+23,13\)
\(=\left(12,34+7,66\right)+\left(23,87+23,13\right)\)
\(=20+47=67\)
c) \(45,09+56,73+54,91+43,27\)
\(=\left(45,09+54,91\right)+\left(56,73+43,27\right)\)
\(=100+100=200\)
d)Sửa đề: \(12,23+24,47+31,18+63,3+68,82\)
\(=\left(12,23+24,47+63,3\right)+\left(31,18+68,82\right)\)
\(=100+100=200\)
a) 145 + 86 + 14 + 55 = ( 145 + 55 ) + (86 + 14 )
= 200 + 100
= 300
b) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = ( 1+9 +2 + 8) + ( 3 + 7 + 4 + 6 ) + 5
= 20 + 20 + 5
= 45
Bài 5:
a: =1/3+2/5
=5/15+6/15
=11/15
b: =6/21+12/21=18/21=6/7
c: =16/24+10/24
=26/24
=13/12
d: =4/12+3/12+10/12
=17/12
e: =19/24-9/24
=10/24
=5/12
f: =8/9-3/9=5/9
g: =9/3+1/3=10/3
k: =15/24+42/24+14/24
=71/24
\(2018\times\frac{3}{4}+2018\times\frac{1}{4}-2018\)
\(=2018\times\left(\frac{3}{4}+\frac{1}{4}-1\right)\)
\(=2018\times0=0\)
B-a:tương tự bài A
b,\(\frac{14}{18}\times\frac{8}{5}-\frac{7}{9}\times\frac{3}{5}\)
\(=\frac{7}{9}\times\frac{8}{5}-\frac{7}{9}\times\frac{3}{5}\)
\(=\frac{7}{9}\times\left(\frac{8}{5}-\frac{3}{5}\right)\)
\(=\frac{7}{9}\times1=\frac{7}{9}\)\
thanks
B-a,\(\frac{3\times125+3\times125}{6\times43+6\times57}=\frac{2\times3\times125}{6\times\left(43+57\right)}\)
\(=\frac{3\times250}{6\times100}=\frac{5}{2\times2}=\frac{5}{4}\)
thanks
\(\left(A+9\right)+\left(A-8\right)+\left(A+7\right)+\left(A-6\right)+\left(A+5\right)+\left(A+44\right)=63,3\)
\(\left(2A+53\right)+\left(2A-1\right)+\left(2A-1\right)=63,3\)
\(6A-51=63,3\)
\(6A=114,3\)
\(A=19,05\)