In the class intervals given as 10-20, 20-30, the number 20 is included in _____ .
Choose the correct answer in each of the following questions: In the class intervals 10-20, 20-30, the number 20 is included in (a) 10-20 (b) 20-30 (c) in each of 10-20 and 20-30 (d) in none of 10-20 and 20-30