diff --git a/session_1/slides_b.Rmd b/session_1/slides_b.Rmd
index f239afe72c60adc2f6a7e1c78d6f3f8d9b24209f..1831f7543252f7d4596f0d11d5892a3345b3900f 100644
--- a/session_1/slides_b.Rmd
+++ b/session_1/slides_b.Rmd
@@ -114,7 +114,7 @@ base_test <- function(x, base){
 
 RStudio offers you great flexibility in running code from within the editor window. There are buttons, menu choices, and keyboard shortcuts. To run the current line, you can
 
-- click on the Run button above the editor panel, or
+- Click on the Run button above the editor panel, or
 - select “Run Lines” from the “Code” menu, or
 - hit Ctrl+Return in Windows or Linux or Cmd+Return on OS X. To run a block of code, select it and then Run. 
 
@@ -281,7 +281,7 @@ all.equal(x, y)
 ## Vector challenge
 
 - use the `seq()` function to create a vector of even numbers
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet.
 - Check the default vectors `letters` and `LETTERS`, rewrite your previous command using them.
 - Create a vector giving you the correspondence between small case letters and upper case letters.
 
@@ -291,7 +291,7 @@ all.equal(x, y)
 ```R
 seq(from=2, to=10, by=2)
 ```
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet. What is the type of this vector.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet. What is the type of this vector.
 - Check the default vectors `letters` and `LETTERS`, rewrite your previous command using them.
 - Create a vector giving you the correspondence between small case letters and upper case letters.
 
@@ -301,14 +301,14 @@ seq(from=2, to=10, by=2)
 ```R
 seq(from=2, to=10, by=2)
 ```
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet. What is the type of this vector.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet. What is the type of this vector.
 - Check the default vectors `letters` and `LETTERS`, rewrite your previous command using them.
 - Create a vector giving you the correspondence between small case letters and upper case letters.
 
 ### Vector challenge
 
 - use the `seq()` function to create a vector of even numbers
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet. What is the type of this vector.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet. What is the type of this vector.
 ```R
 c(1:5, "a", "b", "c")
 typeof(c(1:5, "a", "b", "c"))
@@ -319,7 +319,7 @@ typeof(c(1:5, "a", "b", "c"))
 ### Vector challenge
 
 - use the `seq()` function to create a vector of even numbers
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet. What is the type of this vector.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet. What is the type of this vector.
 - Check the default vectors `letters` and `LETTERS`, rewrite your previous command using them.
 ```R
 c(1:5, letters[1:3])
@@ -329,7 +329,7 @@ c(1:5, letters[1:3])
 ### Vector challenge
 
 - use the `seq()` function to create a vector of even numbers
-- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integer with a vector of the first 5 letter of the alphabet. What is the type of this vector.
+- You can concatenate vector with `c(<VECTOR_1>, <VECTOR_2>)`, concatenate a vector of integers with a vector of the first 5 letters of the alphabet. What is the type of this vector.
 - Check the default vectors `letters` and `LETTERS`, rewrite your previous command using them.
 - Create a vector giving you the correspondence between small case letters and upper case letters.
 ```R
diff --git a/session_2/slides.Rmd b/session_2/slides.Rmd
index 2cd63a353438ba6f8c2c03179ea49483d52a7453..a39dbadfaf44240af321a9a2a58df550df10836c 100644
--- a/session_2/slides.Rmd
+++ b/session_2/slides.Rmd
@@ -185,8 +185,8 @@ ggplot(data = <DATA>) +
 - Run `ggplot(data = new_mpg)`. What do you see?
 - How many rows are in `new_mpg`? How many columns?
 - What does the `cty` variable describe? Read the help for `?mpg` to find out.
-- Make a scatterplot of `hwy` vs `cyl`.
-- What happens if you make a scatterplot of `class` vs `drive`? Why is the plot not useful?
+- Make a scatterplot of `hwy` vs. `cyl`.
+- What happens if you make a scatterplot of `class` vs. `drive`? Why is the plot not useful?
 
 ### Run `ggplot(data = mpg)`. What do you see?
 
@@ -200,14 +200,14 @@ ggplot(data = new_mpg)
 new_mpg
 ```
 
-### Make a scatterplot of `hwy` vs `cyl`.
+### Make a scatterplot of `hwy` vs. `cyl`.
 
 ```{r new_mpg_plot_b, cache = TRUE, fig.width=8, fig.height=4.5}
 ggplot(data = new_mpg) + 
   geom_point(mapping = aes(x = hwy, y = cyl))
 ```
 
-### What happens if you make a scatterplot of `class` vs `drive`?
+### What happens if you make a scatterplot of `class` vs. `drive`?
 Why is the plot not useful?
 
 ```{r new_mpg_plot_c, cache = TRUE, fig.width=8, fig.height=4.5}
@@ -226,7 +226,7 @@ ggplot(data = mpg) +
              mapping = aes(x = displ, y = hwy), color = "red")
 ```
 
-###  Aesthetic mappings `color`
+###  Aesthetic mapping `color`
 
 ```{r new_mpg_plot_e, cache = TRUE, fig.width=8, fig.height=4.5}
 ggplot(data = mpg) + 
@@ -244,21 +244,21 @@ Try the following aesthetic:
 - `alpha`
 - `shape`
 
-###  Aesthetic mappings `size`
+###  Aesthetic mapping `size`
 
 ```{r new_mpg_plot_f, cache = TRUE, fig.width=8, fig.height=4.5, warning=FALSE}
 ggplot(data = mpg) + 
   geom_point(mapping = aes(x = displ, y = hwy, size = class))
 ```
 
-###  Aesthetic mappings `alpha`
+###  Aesthetic mapping `alpha`
 
 ```{r new_mpg_plot_g, cache = TRUE, fig.width=8, fig.height=4.5, warning=FALSE}
 ggplot(data = mpg) + 
   geom_point(mapping = aes(x = displ, y = hwy, alpha = class))
 ```
 
-###  Aesthetic mappings `shape`
+###  Aesthetic mapping `shape`
 
 ```{r new_mpg_plot_h, cache = TRUE, fig.width=8, fig.height=4.5, warning=FALSE}
 ggplot(data = mpg) + 
@@ -385,7 +385,7 @@ ggplot(data = mpg, mapping = aes(x = displ, y = hwy, color = drv)) +
 - What does `show.legend = FALSE` do?
 - What does the `se` argument to `geom_smooth()` do?
 
-## Fird challenge
+## Third challenge
 
 - Recreate the R code necessary to generate the following graph
 
@@ -395,7 +395,7 @@ ggplot(data = mpg, mapping = aes(x = displ, y = hwy, color = drv)) +
   geom_smooth(mapping = aes(linetype = drv))
 ```
 
-## Fird challenge
+## Third challenge
 
 ```{r new_mpg_plot_v, cache = TRUE, fig.width=8, fig.height=4.5, message=FALSE}
 ggplot(data = mpg, mapping = aes(x = displ, y = hwy, color = drv)) +