Tính bằng cách hợp lí nhất. 349+602+651+398

a) \(349 + 602 + 651 + 398\)

\( = \left( {349 + 651} \right) + \left( {602 + 398} \right)\)

\( = 1{\rm{ }}000 + 1{\rm{ }}000\)

\( = 2{\rm{ }}000\).

b) \(3,24 \times 6,34 + 3,24 \times 3,66\)

\( = 3,24 \times \left( {6,34 + 3,66} \right)\)

\( = 3,24 \times 10\)

\( = 32,4.\)

c) \(112,37 \times 4,29 - 4,29 \times 12,37\)

\( = \left( {112,37 - 12,37} \right) \times 4,29\)

\( = 100 \times 4,29\)

\( = 429.\)

d) \(4 \times 113 \times 25 - 5 \times 112 \times 20\)

\( = 4 \times 25 \times 113 - 5 \times 20 \times 112\)

\( = 100 \times 113 - 100 \times 112\)

\( = 100 \times \left( {113 - 112} \right)\)

\( = 100 \times 1\)

\( = 100.\)