a, =12 x ( 45 + 55 )

= 12 x 100 

= 1200

b, = 25 x 4 x 280

= 100 x 280

= 28000

c, = 268 x ( 192 -92)

= 268 x 100

= 26800

Câu 2: Tính bằng cách thuận tiện nhất:

\(a)\)\(12\times45+12\times55\)

\(=\)\(12\times\left(45+55\right)\)

\(=\)\(12\times100\)

\(=\)\(1200\)

\(b)\)\(25\times280\times4\)

\(=\)\(25\times4\times280\)

\(=\)\(100\times280\)

\(=\)\(28000\)

\(c)\)\(268\times192-92\times268\)

\(=\)\(268\times\left(192-92\right)\)

\(=\)\(268\times100\)

\(=\)\(26800\)

Trả lời :

a). 12 x 45 + 12 x 55 = 12 x ( 45 + 55 )

                                  = 12 x 100

                                  = 1200.

b). 25 x 280 x 4 =  280 x ( 25 x 4 )

                          = 280 x 100

                          = 28 000.

c). 268 x 192 - 92 x 268 = 268 x ( 192 - 92 )

                                       = 268 x 100

                                       = 26 800.

Nhớ k cho chị nha , Cảm ơn em.

29,079 x 45 + 29,079 - 46 x 29,079

= 29,079 x (45 + 1 - 46)

= 29,079 x 0 = 0

29.079 x 45 + 29.079 - 46 x 29.079

= 29.079 x 45 + 29.079 x 1 - 46 x 29.079

= 29.079 x (45 + 1 - 46)

= 29 079 x 0

= 0

    57 \(\times\) 46 + 57 \(\times\) 54

= 57    \(\times\) ( 46 + 54)

= 57 \(\times\) 100

= 5700

137 + 355 + 63 + 45

= ( 137 + 63) + ( 355 + 45)

= 200 + 400

= 600

215 \(\times\) 48 - 215 \(\times\) 38

= 215 \(\times\) ( 48 - 38)

= 215 \(\times\) 10

= 2150 

4 \(\times\) 50 \(\times\) 25 

= ( 4 \(\times\) 25) \(\times\) 50

= 100 \(\times\) 50

= 5 000

57×(46+54) =57×100=5700

137+355+63+45=(137+63) +(355+45) =200+400=600

215×48-215×38=215×(48-38) =215×10=2150

4×50×25=(4×25) ×50=100×50=5000

    57 $\times$ 46 + 57 $\times$ 54

= 57    $\times$ ( 46 + 54)

= 57 $\times$ 100

= 5700

137 + 355 + 63 + 45

= ( 137 + 63) + ( 355 + 45)

= 200 + 400

= 600

215 $\times$ 48 - 215 $\times$ 38

= 215 $\times$ ( 48 - 38)

= 215 $\times$ 10

= 2150 

4 $\times$ 50 $\times$ 25 

= ( 4 $\times$ 25) $\times$ 50

= 100 $\times$ 50

= 5 000

a, 49 x 385 - 39 x 385

= 385 x ( 49 - 39)

= 385 x 10

= 3850

b, 46 x 17 + 38 x 46 + 46 x 44 + 46

= 46 x 17 + 38 x 46 + 46 x 44 + 46 x 1

= 46 x (17 + 38 + 44 + 1)

= 46 x 100

= 4600 

\(=46\left(17+38+1+44\right)\)

\(=4600\)

\(=246\times\left(145+1-46\right)=246\times100=2460\)

246 x 145 + 246 - 46 x 246

=256 x (145-46+1)

=246 x 100

=24600

= 246 x ( 145 - 46 + 1 )

= 246 x 100

= 24600

\(25\times4\times46+25\times54\times4\)
\(\Rightarrow25\times4\times\left(46+54\right)\)
\(\Rightarrow100\times100\)
\(\Rightarrow10000\)

25 × 4 × 46 + 25 × 54 × 4 

=25 × 4 × ( 46 + 54 ) 

=100 × 100 

=10000

25 × 4 × 46 + 25 × 54 × 4 

=25 × 4 × ( 46 + 54 ) 

=100 × 100 

=10000