Bài 3 Tính: a) \(217 \times 11\) b) \(413 \times 21\) c) \(1234 \times 31\) \(217 \times 9\) \(13 \t
Bài 3 Tính:
a) \(217 \times 11\) b) \(413 \times 21\) c) \(1234 \times 31\)
\(217 \times 9\) \(13 \times 19\) \(875 \times 29\)
Lời Giải:
Bài 3
a) \(217 \times 11 = 217 \times \left( {10{\rm{ }} + 1} \right) = {\rm{ }}217 \times 10 + 217 \times 1 = 2170 + 217 = 2387\)
\(217 \times 9 = 217 \times \left( {10 - 1} \right) = 217 \times 10 - 217 \times 1 = 2170 - 217 = 1953\)
b) \(413 \times 21 = 413 \times \left( {20{\rm{ }} + {\rm{ }}1} \right) = 413 \times 20 + 413 \times 1 = 8260 + 413 = 8673\)
\(413 \times 19 = 413 \times \left( {20 - 1} \right) = 413 \times 20 - 413 \times 1 = 8260 - 413 = 7847\)
c) \(1234 \times 31 = 1234 \times \left( {30{\rm{ }} + 1} \right) = 1234 \times 30 + 1234 \times 1 = 37020 + 1234 = 38254\)
\(875 \times 29 = 875 \times \left( {30 - 1} \right) = 875 \times 30 - 875 \times 1 = 26250 - 875 = 25375\)