Fourth Grade Students (Use estimation strategies (clustering around an average), and assess the reasonableness of answers in multistep word problems)

In Sara’s school there are 5 classes in 4th grade ,class 1 has 19 students, class 2 has 21 students, class 3 has 23 students, class 4 has 20 students, and class 5 has 19 students. About how many fourth grade students are in the school altogether?