The coefficient of x5 in 3x2+5x310

General term Tr+1=Cr   nan-rbr in the expansion (a+b)nTr+1=Cr   10(3x2)10−r5x3r        =Cr   10310−rx20−2r5rx−3r        =Cr   10310−r5rx20−5r According to problem we need coefficient of x5⇒20−5r=5⇒20−5=5r⇒15=5r⇒r=3∴T3+1=C3   103753