* \(21.15=315\)

* \(275+498=773\)

Nếu so sánh thì ta thấy: \(315< 773\)

Nên \(21.15< 275+498\)

Chúc bạn học tốt và tíck cho mìk vs nha hoanganh!

21x15=315

275+498=773

21x15=315

275+ 498 = 773

   21¹⁵ + 275 x 498

= 21¹⁵ +   136 950

=     137 265

k nha ^_-

a) 89,42 + ( 21,15 + 16,471 ) = 89,42 + 37,621 = 127,041

b) ( 135,8 + 69,07 ) + 52,18 = 204,87 + 52,18 = 257,05

c) ( 89,42 + 21,15 ) + 16,471 = 110,57 + 16,271 = 127,041

d) 135,8 + ( 69,07 + 52,18 ) = 135,8 + 121,25 = 257,05

\(x+53,67=139,5\times12\)

\(x+53,67=1674\)

\(x=1620,33\)

\(x-42,3=21,15+13,7\)

\(x-42,3=34,85\)

\(x=77,15\)

\(7,2+x:4=108\)

\(x:4=100,8\)

\(x=403,2\)

\(x\times4-7,2=10,8\)

\(x\times4=18\)

\(x=4,5\)

x + 53,67 = 139,5 x 12

x+53,67=1674

x=1674-53,67

x=1620,33

x - 42,3 = 21,15 + 13,7

x-42,3=34,85

x=34,85+42,3

x=77,15

7,2 + x : 4 = 108

x:4=108-7,2

x:4=100,8

x=100,8x4

x=403,2

x x 4 -7,2 =10,8

x x 4=10,8+7,2

x x 4=18

x=18:4

x=4,5

`x + 53,67 = 139,5 xx 12`

`=>x + 53,67 = 1674`

`=>x=1674-53,67`

`=>x=1620,33`

`-------`

`x - 42,3 = 21,15 + 13,7`

`=>x - 42,3 =34,85`

`=>x=34,85+42,3`

`=>x=77,15`

`-------`

`7,2 + x : 4 = 108`

`=>x:4=108-7,2`

`=>x:4=100,8`

`=>x=100,8 xx 4`

`=>x=403,2`

`-------`

`x xx 4 -7,2 =10,8`

`=>x xx 4=10,8 + 7,2`

`=>x xx 4= 18`

`=>x=18:4`

`=>x=4,5`

a+b=498

5a+35b=10500

=> 5a+5b+30b=10500

=> 5(a+b)+30b=10500

=>30b=10500-2490=8010

=>b=8010/30=267

 vi 308  và 264  đều chia hết cho x nên x là ước chung của 308 và  264

Các phân số bé hơn 1: \(\frac{5}{6},\frac{14}{21}\)

Xét \(\frac{14}{21}=\frac{2}{3}=\frac{4}{6}< \frac{5}{6}\)

Các phân số lớn hơn 1: \(\frac{8}{7},\frac{51}{42},\frac{4}{3},\frac{15}{14}\)

Xét \(\frac{1}{3}>\frac{1}{7}>\frac{1}{14}\Rightarrow\frac{1}{3}+1>\frac{1}{7}+1>\frac{1}{14}+1\Rightarrow\frac{4}{3}>\frac{8}{7}>\frac{15}{14}\)

Xét \(\frac{17}{14}>\frac{16}{14}>\frac{15}{14}\Rightarrow\frac{51}{42}>\frac{8}{7}>\frac{15}{14}\)

Xét \(\frac{56}{42}>\frac{51}{42}\Rightarrow\frac{4}{3}>\frac{51}{42}\)

Từ đây ta được dãy sắp xếp từ bé đến lớn: \(\frac{14}{21}< \frac{5}{6}< \frac{15}{14}< \frac{8}{7}< \frac{51}{42}< \frac{4}{3}.\)

a) \(\dfrac{17}{8}:\left(\dfrac{27}{8}+\dfrac{-11}{2}\right)\)

\(=\dfrac{17}{8}.\dfrac{-8}{17}\)

\(=-1\)

b) \(7,63.21,15+7,63.\left(-121,15\right)\)

\(=7,63.\left(21,15-121,15\right)\)

\(=7,63.\left(-100\right)\)

\(=-763\)

c) \(\left(-\dfrac{5}{24}-0,75\right):\left(-2\dfrac{7}{8}\right)\)

\(=\left(-\dfrac{5}{24}-\dfrac{3}{4}\right):\left(-\dfrac{7}{4}\right)\)

\(=\dfrac{-23}{24}.\dfrac{-4}{7}\)

\(=\dfrac{23}{42}\).

\(a.\dfrac{17}{8}:\left(\dfrac{27}{8}+\dfrac{-11}{2}\right)\text{=}\dfrac{17}{8}:\dfrac{-17}{8}\text{=}-1\)

\(b.7,63.21,15+7,63.-121,15\text{=}7,63.\left(21,15-121,15\right)\text{=}7,63.-100\text{=}-763\)

\(c.\left(\dfrac{-5}{24}-0,75\right):\dfrac{-23}{8}\text{=}\dfrac{-23}{24}.\dfrac{-8}{23}\text{=}\dfrac{1}{3}\)