Tính nhẩm:

$\eqalign{ & 16 - 8 = ..... \cr  & 14 - 7 = ..... \cr  & 18 - 9 = ..... \cr}$    $\eqalign{& 9 + 8 = ..... \cr & 7 + 6 = ..... \cr & 5 + 7 = ..... \cr}$     $\eqalign{& 12 - 6 = ..... \cr & 4 + 7 = ..... \cr & 17 - 9 = ..... \cr}$ 

$\eqalign{ & 20 - 1 = ..... \cr  & 20 - 5 = ..... \cr  & 20 - 10 = ..... \cr}$