name<-c("김기훈","박수동","원선희","위계영","최동팔","최종열","최종수","김기팔","이상수","강창수")
prin<-c(98,100,50,50,80,90,30,80,65,95)
micro<-c(82,92,45,100,95,60,30,25,70,90)
macro<-c(95,80,75,100,95,60,30,25,70,90)
df<-data.frame(name,prin,micro,macro)

df$sum<-df$prin+df$micro+df$macro
df$mean<-df$sum/3
df$PF<-ifelse(df$mean >= 60, "pass","fail")
df$grade<-ifelse(df$mean >= 90, "A", ifelse(df$mean >= 80, "B", ifelse(df$mean >= 70, "C", ifelse(df$mean >= 60, "D", "F"))))
df
library(openxlsx)
write.xlsx(df, "C:/Users/user/Desktop/b3-ch1-3.xlsx", colNames=T, asTable=F) # write.xlsx 명령어로 지정된 디렉터리에 지정된 이름의 엑셀파일로 저장