\(1235\text{×}6789\text{×}\left(630-315\text{×}2\right)\)

\(=1235\text{×}6789\text{×}\left(630-630\right)\)

\(=1235\text{×}6789\text{×}0=0\)

\(\left(100+67\right)\text{×}67+\left(200-38\right)\text{×}33\)

\(=167\text{×}67+167\text{×}33\)

\(=167\text{×}\left(67+33\right)\)

\(=167\text{×}100=16700\)

\(72+36\text{×}2+24\text{×}3+18\text{×}4+12\text{×}2+168\)

\(=72+72+72+72+24+168\)

\(=\left(72\text{×}4\right)+24+168=288+24+168=480\)

a) \(1235\times6789\times\left(630-630\right)\)

\(=1235\times6789\times0\)

\(=1235\times0\)

\(=0\)

b) \(167\times67+167\times33\)

\(=167\times\left(67+33\right)\)

\(=167\times100\)

=16700

ta có :
bcnn(a,b)=630=>ab=630(akhong chia het cho b) 
ưcln(a,b)=18 
ta coi a=18x , b=18y => xy=630/18=35 
=> x=5, y=7  hoặc x=7, y=5 
=> a=90.b=126 hoặc a=126,b=7

Ta có:

\(ab=630.18=11340\)

Đặt \(a=18m;b=18n\) (Vì \(ƯCLN\left(a;b\right)=18\))

Vì \(a>b;m>n\)

\(\Rightarrow18m.18n=11340\)

\(\Rightarrow18.18.m.n=11340\)

\(\Rightarrow340.m.n=11340\)

\(\Rightarrow mn=11340\div324\)

\(\Rightarrow mn=35=7.5=35.1\)

\(\Rightarrow\left[\begin{matrix}m=7;n=5\\m=35;n=1\end{matrix}\right.\Rightarrow\left[\begin{matrix}a=18m=126;b=18n=90\\a=18m=630;b=18n=18\end{matrix}\right.\)

Vì \(a\) \(⋮̸\) \(b\Rightarrow a=126;b=90\)

Vậy \(a=126;b=90\)

k) 4 x 113 x 25 - 5 x 112 x 20

= (4 x 25) x 113 - (5 x 20) x 112

= 100 x 113 - 100 x 112

= 100 x (113 - 112)

= 100

p) 1235 x 6789 x (630 - 315 x 2) : 1996

= 1235 x 6789 x (630 - 630) : 1996

= 1235 x 6789 x 0 : 1996

= 0

l) 54 x 113 + 45 x 113 + 113

= 113 (54 + 45 + 1)

= 113 x 100

= 11300

u) (500 x 9 - 250 x 18) x (1 + 2 + 3 + ... + 9)

= (2 x 250 x 9 - 250 x 2 x 9) x (1 +2 + 3 + ... + 9)

= 0 x (1 + 2 + 3 + ... + 9)

= 0

x + 630 = 630 + 1000

x + 630 = 1630

x          = 1630 - 630

x          = 1000

x + 630 = 630 + 1000

x + 630 = 1630

x          = 1630 - 630

x          = 1000

x + 630 = 250 + 630

x + 630 = 880

x = 880-630

x = 250

x + 630 = 250 + 630

=> x + 630 =880

=> x = 880 - 630 

=> x = 250

kết quả là a=54,b=126

Đáp án cần chọn là: D

UCLN chứ nhỉ =))

uk