A surveyor measured the distance between two points on the plan drawn to a scale of $1 \mathrm{~cm}=40 \mathrm{~m}$ and the result was 468 m . Later, it was discovered that the scale used was $1 \mathrm{~cm}=20 \mathrm{~m}$.

The true distance between the points (in m ) is __________ (round off to the nearest integer).

For a reconnaissance survey, it is necessary to obtain vertical aerial photographs of a terrain at an average scale of 1: 13000 using a camera. If the permissible flying height is assumed as 3000 m above a datum and the average terrain elevation is 1050 m above the datum, the required focal length (in mm) of the camera is

A line between stations P and Q laid on a slope of 1 in 5 was measured as 350 m using a 50 m tape. The tape is known to be short by 0.1 m.

The corrected horizontal length (in m) of the line PQ will be

A map is prepared with a scale of 1:1000 and a contour interval of 1 m. If the distance between two adjacent contours on the map is 10 mm, the slope of the ground between the adjacent contours is