If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55, 60, then the average marks of all the students is:
Answer: B
Required average
\(\left( \dfrac {55 \times 50 + 60 \times 55 + 45 \times 60}{55+60+45} \right)\\
=\left( \dfrac {2750 + 3300 + 2700}{160} \right)\\
=\dfrac{8750}{160}\\
=54.68\)