\(201905139B⋮12\) khi đồng thời chia hết cho 3 và 4

\(201905139B⋮12\) Khi\(\overline{9B}⋮4\) => B=2 hoặc B=6 

=> B chẵn

\(201905139B⋮3\Rightarrow2+1+9+5+1+3+9+B=30+B⋮3\)

=> B=0 hoặc B=3 hoặc B=6 hoặc B=9

=> B=6 thỏa mãn đk đề bài

 y × $\frac{14}{9}$ - y × $\frac{7}{9}$ + y × $\frac{5}{9}$ = 2

$\text{y × (}$ $\frac{14}{9}$ - $\frac{7}{9}$ + $\frac{5}{9}$ $\text{) = 2}$

$\text{y ×}$ $\frac{12}{9}$ $\text{= 2}$

$\text{y = 2 ÷}$ $\frac{12}{9}$

$\text{y =}$ $\frac{2}{1}$ x $\frac{12}{9}$

$\text{y =}$ $\frac{3}{2}$

\(B=1+2+4+5+7+8+10+...+119+121+122\)

Ta có : 

\(A=1+2+3+...+121+122\)

\(A=\left[\left(122-1\right):1+1\right]\left(1+122\right):2\)

\(A=122.\left(123\right):2=7503\)

Ta lại có :

\(C=3+6+9+...+120\)

\(C=\left[\left(120-3\right):3+1\right]\left(3+120\right):2\)

\(C=40.123:2=2460\)

Ta thấy : \(B=A-C\)

\(B=7503-2460=5043\)

\(y\times\dfrac{6}{11}+y\times\dfrac{5}{11}=2025\)

\(y\times\left(\dfrac{5}{11}+\dfrac{6}{11}\right)=2025\)

\(y\times1=2025\)

\(y=2025\)

\(y.\dfrac{6}{11}+y.\dfrac{5}{11}=2025\)

\(y.\left(\dfrac{6}{11}+\dfrac{5}{11}\right)=2025\)

\(y.\left(\dfrac{11}{11}\right)=2025\)

\(y=2025\)

Dấu . là dấu nhân

a) 463+318+137+22

 = (463+137)+(318+22)

 =  600+340

 = 940

b) 185.32-32.85

 =  32.(185-85)

 =  32 . 100

 =  3200

c) \(15:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)

\(\text{= }15:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(\text{= }15:\left\{390:\left[500-370\right]\right\}\)

\(=15:\left(390:130\right)\)

\(\text{= }15:3\)

\(\text{= }5\)

a)\(463+318+137+22\)

\(=\left(463+137\right)+\left(318+22\right)\)

\(=600+340=940\)

b)\(185.3^2-3^2.85\)

\(=3^2.\left(185-85\right)\)

\(=9.100=900\)

c)\(15:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)

\(=15:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(=15:\left\{390:\left[500-370\right]\right\}\)

\(=15:\left\{390:130\right\}\)

\(=15:3=5\)

` a,` 

`1/3 + 3/4 xx 5/9 `

`=1/3 + (3/4 xx 5/9) `

`= 1/3 + 5/12 `

`= 4/12 + 5/12`

`= 9/12 `

`= 3/4 .`

`b,`

` 7/12 - 5/4 xx 2/15 `

`= 7/12 - (5/4 xx 2/15)`

`= 7/12 - 1/6`

`= 7/12 - 2/12 `

`= 5/12 .`