Missing number is 6. All opposite numbers add up to 21.

缺少的数字是6，每组相对数字的和为21。 。

youdao

There were fears the death toll could rise sharply with estimates of the number of missing varying from 54 to 67.

人们担心根据估计的失踪人数，死亡人数可能会急速上升为54到67人。

youdao

The number of “missing girls” doubled in Europe and Central Asia (mainly in the Balkans and the Caucasus), from a low base.

在欧洲和中亚“失踪女性”的数量从原本的低基数翻了一倍（主要是在巴尔干半岛和高加索地区）。

youdao

Only the bomber was killed. In the restive northern Iraqi city of Mosul, a grenade was also thrown at a U.S.patrol, reportedly missing the U.S.soldiers, but killing a number of Iraqi civilians.

VOA: standard.2009.06.01

Shoddy kicking was a feature of the encounter, Danny Cipriani missing a number of penalty attempts on his first start since breaking a leg in October.

BBC: Harlequins 20-21 Wasps

Behrami should have added a second but hit the bar from five yards out, while Sunderland striker Cisse was guilty of missing a number of chances.

BBC: Sunderland 0-1 West Ham

Despite missing a number of players through injury, which saw keeper Brown in for Paul Robinson, Blackburn were starting to rattle their London guests with a number of crunching tackles.

BBC: El-Hadji Diouf celebrates his equaliser