She had known Max for some years now, but he was still pretty much an unknown quantity.

她现在认识马克斯也好几年了，但是他仍然是个大大的未知数。

《柯林斯英汉双解大词典》

One advantage of sticking with the current version: it's a known quantity, and plenty of review materials exist.

坚持考老版本SAT的好处是：我们对这个考试有充分的了解，市面上充盈着丰富的复习资料。

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The third step in estimating is to use the concept and the model to provide a comparison with the known quantity.

第三步是用估算的概念和模式提供了一个比较有噪。

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Hardly an inspiring way of choosing a candidate, but Republicans apparently like a known quantity.

FORBES: Bye Bye Beijing, Hello White House?

G. was such a known quantity, how on Earth is someone going to fill those shoes?

NPR: Lifestyle & Trends: Kanye West, 50 Cent Do Battle

By contrast, the PPI payments were, by the time of the Budget, very much a known quantity.

BBC: A welcome boost - unless you're a bank