1.

$\square \bigcirc \square =\square$(支)

$14 - 7 = 7$

2. 用竖式计算。
$78-51= $ $43+16= $ $59+5= $
$42-9= $ $17+54= $ $80-27= $

27 59 64 33 71 53

3. 神奇的算式。
$18+81= \square$ $99-18= \square$
$27+72= \square$ $99-27= \square$
$36+\square=\square$ $99-\square=\square$
$\square+\square=\square$ $\square-\square=\square$
$\square+\square=\square$ $\square-\square=\square$
$\square+\square=\square$ $\square-\square=\square$
$\square+\square=\square$ $\square-\square=\square$
$\square+\square=\square$ $\square-\square=\square$

99 99 63 99 $45 + 54 = 99$ $54 + 45 = 99$ $63 + 36 = 99$ $72 + 27 = 99$ $81 + 18 = 99$ 81 72 36 63 $99 - 45 = 54$ $99 - 54 = 45$ $99 - 63 = 36$ $99 - 72 = 27$ $99 - 81 = 18$