三年级有20个同学参加竞赛，其中参加数学竞赛的有15人，参加作文竞赛的有13人，既参加数学竞赛又参加作文竞赛的有几人？
直接写得数．×= 1﹣= 7+6.2=÷1=÷=×= 2.5×=×=
直接写出答案========
×=÷6=
直接写得数÷7= 42×= 6÷=×33=÷=+= 10÷1%=﹣20%=﹣= 24×50%=
直接写出得数．= 15=== 0.33==== 1﹣====
×
= 1﹣
= 7+6.2=
÷1=
÷
=
×
= 2.5×
=
×
=
=
=
=
=
=
=
=
=
×
=
÷6=
÷7= 42×
= 6÷
=
×33=
÷
=
+
= 10÷1%=
﹣
= 24×50%=
= 15
=
=
=
=
=
=
=
=
=
=
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