Question

bài 1: tính nhanh

a. 30 x 1235 x 4 - 8 x 235 x 15

b. ( 120 x 99 + 120 ) - 185 x 101 - 185

Answer 1

a) \(30\times1235\times4-8\times235\times15\)

\(=120\times1235-120\times235\)

\(=120\times\left(1235-235\right)\)

\(=120\times1000\)

\(=120000\)

b) \(\left(120\times99+120\right)-185\times101+185\)

\(=120\times\left(99+1\right)-185\cdot\left(101-1\right)\)

\(=120\times100-185\times100\)

\(=12000-18500\)

\(=-6500\)

Answer 2

a) 30 x 1235 x 4 - 8 x 235 x 15

=(30x4) x 1235 - (8x15)x235

= 120 x 1235 - 120 x 235

=120 x (1235-235)

=120 x 1000

=120000

b) ( 120 x 99 +120)  - 185 x 101-185

=(120 x 99 + 120) - (185x101+185)

=120x(99+1) - 185x(101+1)

=120 x 100-185x102

=12000-18870

= -(18870-12000)

= -6870