tính giá trị biểu thức : 9900 : 36 - 15
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9900 : 36 - 15 x 11
= 275 - 165
= 110
9700 : 100 + 36 x 12
= 97 + 432
= 529
( 15792 : 336 ) x 5 + 27 x 11
= 47 x 5 + 297
= 235 + 297
= 532
( 160 x 5 - 25 x 4 ) : 4
= ( 800 - 100 ) : 4
= 700 : 4
= 175
1036 + 64 x 52 - 1827
= 1036 + 3328 - 1827
= 4364 - 1827
= 2537
215 . 869 + 215 . 14
= 215 . ( 869 + 14 )
= 215 . 883
= 189945
A = \(\dfrac{1}{12}\)+ \(\dfrac{1}{20}\)+ \(\dfrac{1}{30}\)+...+\(\dfrac{1}{9900}\)
A = \(\dfrac{1}{3\times4}\)+ \(\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+...+\dfrac{1}{99\times100}\)
A = \(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{99}-\dfrac{1}{100}\)
A = \(\dfrac{1}{3}\) - \(\dfrac{1}{100}\)
A = \(\dfrac{97}{300}\)
Lời giải:
Gọi tổng trên là $A$
$A=\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+....+\frac{1}{99.100}$
$=\frac{4-3}{3.4}+\frac{5-4}{4.5}+\frac{6-5}{5.6}+...+\frac{100-99}{99.100}$
$=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{99}-\frac{1}{100}$
$=\frac{1}{3}-\frac{1}{100}=\frac{97}{300}$
`A=1/2+1/6+1/12+1/20+1/30+...+1/9900`
`=1/(1xx2)+1/(2xx3)+1/(3xx4)+1/(4xx5)+1/(5xx6)+...+1/(99xx100)`
`=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+...+1/99-1/100`
`=1/1-1/100`
`=100/100-1/100`
`=99/100`
A=1/2+1/6+1/12+1/20+1/30+...+1/9900
=1/(1��2)+1/(2��3)+1/(3��4)+1/(4��5)+1/(5��6)+...+1/(99��100)=1/(1xx2)+1/(2xx3)+1/(3xx4)+1/(4xx5)+1/(5xx6)+...+1/(99xx100)
=1/1−1/2+1/2−1/3+1/3−1/4+1/4−1/5+1/5−1/6+...+1/99−1/100=1/1−1/2+1/2−1/3+1/3−1/4+1/4−1/5+1/5−1/6+...+1/99−1/100
=1/1−1/100=1/1−1/100
=100/100−1/100=100/100−1/100
=99/100=99/100
a) 397,5 : 7,5 x 10,5 =53 x 10,5 = 556,5
b) 36 : 15 x 5,4 = 2,4 x 5,4 = 12,96
ta có:
1/2+1/6+...+1/9900
=1/1.2+1/2.3...+1/99.100
=1-1/2+1/2-1/3+1/3-...+1/99-1/100
=1-1/100
=99/100
\(A=\frac{1}{2}+\frac{1}{6}+\cdot\cdot\cdot+\frac{1}{9900}\)
\(A=\frac{1}{1\times2}+\frac{1}{2\times3}+\cdot\cdot\cdot+\frac{1}{99\times100}\)
\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\cdot\cdot\cdot+\frac{1}{99}-\frac{1}{100}\)
\(A=1-\frac{1}{100}\)
\(A=\frac{99}{100}\)
a; 54 : 72 x 18 : 15
= 0,75 x 18 : 15
= 0,75 x 1,2
= 0,9
b, 25 : 8 x 36 : 50
= (25 : 50) x (36 : 8)
= 0,5 x 4,5
= 2,25
=
Giải thích các bước giải:
9900 : 36 - 15 x 11
= 275 - 165
= 110
9700 : 100 + 36 x 12
= 97 + 432
= 529
( 15792 : 336 ) x 5 + 27 x 11
= 47 x 5 + 297
= 235 + 297
= 532
( 160 x 5 - 25 x 4 ) : 4
= ( 800 - 100 ) : 4
= 700 : 4
= 175