18. Shooting is carried out from the point O along the straight line OX. The average range of the projectile is 1200 m. Assuming that the range H is distributed according to the normal law with an average square deviation of 40 m, find what percentage of the projectiles produced will give flight from 60 to 80 m.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)