①3.6-2.8+7.4-7.2
=3.6+7.4-(2.8+7.2)
=11-10
=1;
②
÷23+8 17
×1 23
+9 17
1 23
=
×8 17
+1 23
×1 23
+9 17
×11 23
=(
+8 17
+1)×9 17
1 23
=2×
1 23
=
;2 23
③(
+1 2
)÷1 3
-3 5
17 18
=
÷5 6
-3 5
17 18
=
-25 18
17 18
=
;4 9
④18÷[
+(5 6
-5 8
)]1 3
=18÷(
+5 6
)7 24
=18÷
27 24
=16.