Mean of a combined group of 50 students?

Question

Professor Abel corrected 20 papers and found the mean to be 70. He then corrected 30 more papers and found the mean for this group to be 80. What is the mean of the combined group of 50 students?

Answer 1

(20*70 + 30*80)/50

=(1400 + 2400)/50

=3800/50

=76

Answer 2

the total score for the group of 20 was 1400:

1400/ 20 = 70

the total score for the group of 30 was 2400:

2400/ 30= 80

so the mean for all those grades together would be:

1400 + 2400 / 50 = mean

3800 / 50= 76

76 is the answer!

Answer 3

(20 * 70 + 30 * 80) / 50

(20 * 7 + 30 * 8) / 5

(4 * 7 + 6 * 8)

28 + 48

76