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