How are 15/40 equal to 3/8? how are 18/30 equal to 6/10 ?
How are 48 equal to 12/16?
How are 2/7 equal to 18/63

Answer is in the file below

tinyurl.com/wpazsebu

60% used a pencil..that leaves  40% remaining students (100% - 60% = 40%)
half of those used a red pen...so 20% used a red pen. (40% / 2 = 20%)
6 students used a red pen. so... 6 students is 20% of what number ?
6 = 0.20x
6/0.20 = x
30 = x
There are 30 students in the class