1.用“”画出下面每题先算什么,再计算。
$68-24×2$
$=(\quad)○(\quad)$
$=(\quad)$
$56-3×13$
$=(\quad)○(\quad)$
$=(\quad)$
$40×2-12$
$=(\quad)-(\quad)$
$=(\quad)$

$68-24×2$
$=68-48$
$=20$
$56-3×13$
$=56-39$
$=17$
$40×2-12$
$=80-12$
$=68$

2.计算下面各题。
$76-4×12$
$3×33-18$
$80-9×7$
$92-3×30$
$65-14×2$
$8×8-27$

28 81 17 2 37 37(过程略)

3.在$□$里填上合适的数，并在横线上列出综合算式。
$\begin{array}{l}\boxed{}× 3\\ \underbrace{\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}}_{21}-\boxed{5}\\ \hspace{1.5em}\boxed{}\end{array}$
$\begin{array}{l}2× 43\\ \underbrace{\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}}_{$$}-30\\ \hspace{1.5em}\boxed{}\end{array}$
$\begin{array}{l}8× 11\\ \underbrace{\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}}_{\boxed{}}-\underbrace{\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}\hspace{0.278em}}_{\boxed{}}\\ \hspace{2.5em}12\end{array}$

7 16 $7×3-5=16$
86 56 $2×43-30=56$
100 88 $100-8×11=12$

4.给8件图中这样的衬衫缝完纽扣后,还剩多少个纽扣？

$50-5×8=10$(个)
答:还剩 10 个纽扣。