tính nhanh
( 4356 + 7685 - 34,78 x 56,7 ) x ( 20 x 5 - 100 )
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9720:216 x 25 + 801,7
= 45 x 25 + 801,7
= 1125 + 801,7
= 1926,7
56,7 + 48x 56 : 112
= 56,7 + 2688:112
=56,7 + 24
= 80,7
2,4 x 45,6 + 2,4 x 53,1 + 2,4 x 1,3
2,4 x ( 45,6 + 53,1 + 1,3 )
2,4 x 100
240
\(58\times120-20\times58\)
\(=58\times\left(120-20\right)\)
\(=58\times100\)
\(=5800\)
Bài 2:
a: =47,4+47,4x4=47,4x5=237
b: =(0,26+0,74)+(0,41+0,59)=1+1=2
= ( 101 x 37 x 50 - 101 x 50 x 36 ) : ( 1 + 2 + 3 + ............. + 100 )
= ( 101 x 1850 - 101 x 1800 ) : ( 1 + 2 + 3 + ............. + 100 )
= [ 101 x ( 1850 - 1800 )] : ( 1 + 2 + 3 + ............. + 100 )
= [ 101 x 50 ] : ( 1 + 2 + 3 + ............. + 100 )
= 5050 : 5050
= 1
T - I - C - K mk nha
chúc bạn học tốt ~
a) 3/7 + 4/9 + 4/7 + 5/9
= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )
= 7/7 + 9/9
= 1 + 1
= 2
b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5
= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5 ) + 5/5
= 2 + 2 + 2 + 2 + 1
= 2 x 4 + 1
= 8 +1
= 9
c) 1/8 + 1/12 + 3/8 + 5/12
= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)
= 4/8 + 6/12
= 1/2 + 1/2
= 2/4 = 1/2
mỏi tay rồi
d; (1 - \(\dfrac{1}{2}\)) x (1 - \(\dfrac{1}{3}\)) x (1 - \(\dfrac{1}{4}\)) x ... x ( 1 - \(\dfrac{1}{100}\))
= \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\) x \(\dfrac{3}{4}\) x \(\dfrac{3}{4}\) x ... x \(\dfrac{99}{100}\)
= \(\dfrac{1}{100}\)
\(A=20\times21+21\times22+...+99\times100\)
\(3\times A=20\times21\times\left(22-19\right)+21\times22\times\left(23-20\right)+...+99\times100\times\left(101-98\right)\)
\(=20\times21\times22-19\times20\times21+...+99\times100\times101-98\times99\times100\)
\(=99\times100\times101-19\times20\times21\)
Suy ra \(A=\frac{99\times100\times101-19\times20\times21}{3}=360640\)
\(B=3\times4\times5+4\times5\times6+...+98\times99\times100\)
\(4\times B=3\times4\times5\times\left(6-2\right)+4\times5\times6\times\left(7-3\right)+...+98\times99\times100\times\left(101-97\right)\)
\(=3\times4\times5\times6-2\times3\times4\times5+...+98\times99\times100\times101-97\times98\times99\times100\)
\(=98\times99\times100\times101-2\times3\times4\times5\)
Suy ra \(B=\frac{98\times99\times100\times101-2\times3\times4\times5}{4}=24497520\)
Tính nhanh :
165 x 23 - 65 x 23
= 23 x ( 165 - 65 )
= 23 x 100
= 2300
136 + 63 + 100
= 199 + 100
= 299
165 -20 - 65
= ( 165 - 65 ) - 20
= 100 - 20
= 80
165 x 23 - 65 x 23 = ( 165 - 65 ) x 23 = 100 x 23 = 2300
136 + 63 + 100 = 199 + 100 = 299
165 - 20 - 65 = 165 - 65 - 20 = 100 - 20 = 80
( 4356 + 7685 - 34,78 x 56,7 ) x ( 20 x 5 - 100 )
=( 4356 + 7685 - 34,78 x 56,7)x (100-100)
= ( 4356 + 7685 - 34,78 x 56,7)x 0
=0
k mk nhá
( 4356 + 7685 - 34,78 x 56,7 ) x ( 20 x 5 - 100 )
= ( 4356 + 7685 - 34,78 x 56,7 ) x 0
= 0