gradestv <-
structure(list(tv = c(0L, 0L, 0L, 5L, 7L, 10L, 11L, 12L, 14L, 
15L, 15L, 16L, 17L, 19L, 20L, 20L, 20L, 23L, 24L, 25L, 27L, 28L, 
30L, 30L, 32L), grades = c(82L, 93L, 65L, 90L, 85L, 100L, 90L, 
95L, 84L, 75L, 75L, 90L, 79L, 75L, 85L, 78L, 80L, 67L, 75L, 70L, 
68L, 63L, 60L, 65L, 85L)), row.names = c(NA, -25L), class = c("tbl_df", 
"tbl", "data.frame"))