R Notebook

english <- c(90,80,82,33,33,2,22,33,44,22)
math <- c(90,80,82,33,33,2,22,33,433,22)
science <- c(90,80,82,33,33,2,22,33,44,33)
total <- df.score$english+df.score$math+df.score$science
mean <- (df.score$english+df.score$math+df.score$science)/3
df.score <- data.frame(english,math,science,total,mean)
df.score

df.score$A <- ifelse(df.score$mean >= 50.00000, "A",
                     ifelse(df.score$mean >= 25, "B",
                            ifelse(df.score$mean >= 20, "C", "D")))
df.score$A

 [1] "A" "A" "A" "B" "B" "D" "C" "B" "A" "B"

```