有甲、乙、丙三个人，当甲的年龄是乙的2倍时，丙是22岁；当乙的年龄是丙的2倍时，甲是31岁；当甲60岁时，丙是多少岁？
用递等式计算．．
直接写出得数+= 1÷=×=÷9= （﹣0.5）÷=÷=×=÷10=﹣=÷×=
口算：+= 3﹣2= 1÷1= 7×÷7×= 5÷5=×1.2=×1=（+）×20=
直接写得数． 4÷40%=×= 20×5.5=（+）×4=﹣= 2.9+3.4= 0.1÷0.01= 6﹣﹣=÷3= 6×=÷= 1÷﹣÷1=
直接写出得数+=×= 1﹣20%﹣= 4×==+25%= 3﹣==
．
+
= 1÷
=
×
=
÷9=
﹣0.5）÷
=
÷
=
×
=
÷10=
﹣
=
÷
×
=
+
= 3﹣2
= 1
÷1= 7×
÷5=
×1.2=
×1
=（
+
）×20=
×
= 20×5.5=（
+
）×4=
﹣
= 2.9+3.4= 0.1÷0.01= 6﹣
﹣
=
÷3= 6×
=
÷
= 1÷
﹣
÷1=
+
=
×
= 1﹣20%﹣
= 4×
=
=
+25%= 3﹣
=
=
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