∵一班捐款630元,二班比一班少捐款100元,∴二班捐款数=630-100=530元.∵三班捐款数是年级总数的20％,∴三班捐款数=6300*20%=1260元.∴四班,五班捐款数之和=6300-1260-630-530=3880元.∵四班与五班捐款数之比是6比7,...