Question

Ruma's average mark in 5 subject is 60. She secured 100 in maths and 80 in science .the averege markes in remaining 3 subject is
1-40,2-60,3-45,4-none

Answer 1

$\frac{sum \: of \: 5 \: subjects}{5} = 60 \\ sum \: of \: 5 \: subjects = 300 \\ maths + science + 3 \: subjects = 300 \\ 100 + 80 + 3 \: subjects = 300 \\ 3 \: subjects = 300 - 100 - 80 \\ 3 \: subjects = 120$

Now,
Average of other 3 subjects,

$= \frac{sum \: of \: 3 \: subjects}{3} \\ = \frac{120}{3} \\ 40$

Answer is 1. 40