钢琴的黑键有36个，比白键少16个，白键有多少个？
计算．﹣=﹣=+=+=﹣1=﹣=+=﹣= 1﹣=
计算．﹣（）+++（﹣）﹣﹣．
直接写得数：+=﹣=﹣=﹣= 1﹣=+=+=+=﹣= 2﹣=
直接写得数．+=﹣= 1﹣=+=+=+=
3﹣++ 5﹣+﹣1．
﹣
=
﹣
=
+
=
+
=
﹣1=
﹣
=
+
=
﹣
= 1
﹣
﹣（
）
+
+
+（
﹣
）
﹣
．
+
=
﹣
=
﹣
=
﹣
= 1﹣
=
+
=
+
=
+
=
= 2﹣
+
=
﹣
= 1﹣
=
+
=
+
=
+
﹣
+
+
5﹣
+
﹣1．
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