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
What is the CORRECT match between the survey instruments/parts of instruments shown in the table and the operations carried out with them?
| Instruments/Parts of instruments | Operations |
|---|---|
| P - Bubble tube | i - Tacheometry |
| Q - Plumb bob | ii - Minor movements |
| R - Tangent screw | iii - Centering |
| S - Stadia cross-wire | iv - Levelling |
To finalize the direction of a survey, four surveyors set up a theodolite at a station P and performed all the temporary adjustments. From the station P, each of the surveyors observed the bearing to a tower located at station Q with the same instrument without shifting it. The bearings observed by the surveyors are 30° 30' 00", 30° 29' 40", 30° 30' 20" and 30° 31' 20". Assuming that each measurement is taken with equal precision, the most probable value of the bearing is
A child walks on a level surface from point P to point Q at a bearing of 30°, from point Q to point R at a bearing of 90° and then directly returns to the starting point P at a bearing of 240°. The straight-line paths PQ and QR are 4 m each. Assuming that all bearings are measured from the magnetic north in degrees, the straight-line path length RP (in meters) is ______________ (rounded off to the nearest integer).