Maths question for you all . . .

[charlescpp]

i think 一倍 = x1

比如，A比B多一倍，那么A = B*2，相当于A是B的两倍

[Tanyfei]

It has didnt use the 番 In offical chinese.

dont use that expression.

if you use 倍, everybody can understand you

[roddy]

Well someone thinks

一倍 = 2x

and someone else thinks

一倍 = x1

so saying

if you use 倍, everybody can understand you

appears to be a bit dubious.

[chenpv]

公司B此次采购金额应该在公司A的一倍以上

Should be: 公司B此次采购金额应该比公司A多一倍以上。

More examples from Baidu:

我国癌症患者存活比例提高一倍以上.

一致药业：季报预增一倍以上.

海归：国内国外薪酬相差一倍以上.

为什么比现在林林总总的宽带要贵一倍以上.

城市人均用水量超过农村一倍以上.

Though there are exceptionals, So great to see that the majority native speakers know how to use '倍'.

EDIT: Right, nearly forgot, if the someone wants to use '在一倍以上。' , IMHO, the sentence should be rewritten as:

公司B此次采购金额增额应该在公司A的一倍以上.

[Quest]

一倍 and 两倍 can often be used interchangeably because in most cases, it is illogical to say somethign is 1x the amount of another, one would say "same amount" instead.

The following sentences basically mean the same thing.

他们的人数是你们的一倍.

他们的人数是你们的两倍.

http://www.google.com/search?hl=en&lr=&q=%22%E7%9A%84%E4%B8%80%E5%80%8D%22&btnG=Search

I do agree with chenpv, however, that the correct usage for 2x should be 多/增加/提高/increase 一倍, but may I and can I...

[chenpv]

I agree with Quest that for most Chinese, those two expressions are somewhat interchangeable, because it is commonly understood that '倍' itself contains the meaning of accumulation or addition. In oral Chinese, there couldnt be any perplexity in whatever way someone is expressing himself. But when it comes to official document, contract etc, the more standard usage is favorable, in case foxy guys play words game on it.