Question

The traffic police recorded the speed (in km/h) of $10$ motorists as $47$, $53$, $49$, $60$, $39$, $42$, $55$, $57$, $52$, $48$. Later on an error in the recording instrument was found. Find the correct average speed of the motorists if the instrument recorded the speed $5$ km/h less in each case.

• A. $50$km/hr
• B. $55.2$km/hr
• C. $77.6$km/hr
• D. $83.6$km/hr

Answer 1

Answer: (B)

$55.2$km/hr

Total speed recorded in km/hr$=47+53+49+60+39+42+55+57+52+48$

$=502$

Total number of motorist $=10$

$Average=\frac{Sumofallnumbers}{Numberofitems}$

$\because 5km/hr$ was recorded less in each case due to error in instrument.

$\Rightarrow errordeviation=5\times 10=50$ km\hr

$\therefore$ correct average speed $=\frac{502+50}{10}=55.2$ km\hr

hence, option $B$ is correct.