The correct answer is (c).
A decile is a value that divides a ranked data set into ten equal parts. The first decile (D1) is the value that divides the bottom 10% of the data set from the top 90%. The second decile (D2) is the value that divides the bottom 20% of the data set from the top 80%, and so on.
In this case, the scores are:
43, 56, 35, 47, 48, 52, 66, 57, 46, 39, 43, 47, 61, 55, 50, 49, 39, 40
The deciles are:
D1 = 39
D2 = 43
D3 = 46
D4 = 47
D5 = 48
D6 = 50
D7 = 52
D8 = 55
D9 = 56
D10 = 61
The most popular decile is D4, which has 5 scores: 46, 47, 48, 50, and 52.
The other deciles have fewer scores:
D1 has 1 score: 39
D2 has 2 scores: 43 and 46
D3 has 2 scores: 47 and 48
D5 has 2 scores: 50 and 52
D6 has 1 score: 55
D7 has 1 score: 56
D8 has 1 score: 61
D9 has 1 score: 66
Therefore, the most popular decile is D4.