If you want to get the unknown number, you should know the known number first.

如果要想求出未知数，你首先得知道已知数。

A known number rectangular area is a Y square centimetre, one side is long for X is that this rectangular circumference is several centimetres centimetre.

已知一个长方形的面积为Y平方厘米，一边长为X厘米，则这个长方形的周长为几厘米。

By report, US na German is a known number of in the world only's develop this strange disease clan, but the whole world 'nothing fingerprint people' final total does not exceed 20!

据悉，美娜德一家是世界上惟一已知的患有这种怪病的家族，而全世界的“无指纹人”总计不超过20个！