UPSC NDA Math Model Paper 6

Given that, average marks obtained by the students in a class (XBG)=43
Total number of boys (nB)=25
Average marks obtained by boys (XB)=40
Average marks obtained by girls (Xrm‌C)=48
Let the total number of girls =nG
Now, by formula,
XBG=

nB×XB+nG×XG

nB+nG

⇒43=

25×40+nG×48

25+nG

1075+43×nG=1000+48×nG
⇒75=5nG⇒nG=15
∴ Required number of girls =15