Giải bài 1, 2, 3, 4 trang 48 vở bài tập toán 2 tập 2 - Tính nhẩm :

1.Tính nhẩm :

\(1 \times 2 = .......\) \(1 \times 3 = .......\) \(1 \times 4 = .......\) \(1 \times 5 = .......\)

\(1 \times 1 = .......\) \(2 \times 1 = .......\) \(3 \times 1 = .......\) \(4 \times 1 = .......\)

\(5 \times 1 = .......\) \(1:1 = .......\) \(2:1 = .......\) \(3:1 = .......\) \(4:1 = .......\) \(5:1 = .......\)

2.Số ?

3.Tính

a)

\(\eqalign{ & 2 \times 3 \times 1 = ................ \cr & {\rm{ = }}................. \cr} \) \(\eqalign{ & 2 \times 1 \times 3 = ................ \cr & {\rm{ = }}................. \cr} \)

b)

\(\eqalign{ & 4 \times 5:1 = ................ \cr & {\rm{ = }}................. \cr} \) \(\eqalign{ & 4:1 \times 5 = ................ \cr & {\rm{ = }}................. \cr} \)

c)

\(\eqalign{ & 8:4 \times 1 = ................ \cr & {\rm{ = }}................. \cr} \) \(\eqalign{ & 8 \times 1:4 = ................ \cr & {\rm{ = }}................. \cr} \)

d)

\(\eqalign{ & 12:3:1 = ................ \cr & {\rm{ = }}................. \cr} \) \(\eqalign{ & 12:1:3 = ................ \cr & {\rm{ = }}................. \cr} \)

Giải

1.Tính nhẩm :

\(1 \times 2 = 2\) \(1 \times 3 = 3\)

\(1 \times 4 = 4\) \(1 \times 5 = 5\)

\(1 \times 1 = 1\) \(2 \times 1 = 2\)

\(3 \times 1 = 3\) \(4 \times 1 = 4\)

\(5 \times 1 = 5\) \(1:1 = 1\) \(2:1 = 2\)

\(3:1 = 3\) \(4:1 = 4\) \(5:1 = 5\)

2.Số ?

3.Tính

a)

\(\eqalign{ & 2 \times 3 \times 1 = 6 \times 1 \cr & {\rm{ = 6}} \cr} \) \(\eqalign{ & 2 \times 1 \times 3 = 2 \times 3 \cr & {\rm{ = 6}} \cr} \)

b)

\(\eqalign{ & 4 \times 5:1 = 20:1 \cr & {\rm{ = 20}} \cr} \) \(\eqalign{ & 4:1 \times 5 = 4 \times 5 \cr & {\rm{ = 20}} \cr} \)

c)

\(\eqalign{ & 8:4 \times 1 = 2 \times 1 \cr & {\rm{ = 2}} \cr} \) \(\eqalign{ & 8 \times 1:4 = 8:4 \cr & {\rm{ = 2}} \cr} \)

d)

\(\eqalign{ & 12:3:1 = 4:1 \cr & {\rm{ = 4}} \cr} \) \(\eqalign{ & 12:1:3 = 12:3 \cr & {\rm{ = 4}} \cr} \)