Question

The table below given the seasonal indices for enrollments of students in a mathematics subject at Tsinghua University over three trimesters

Trimester	1	2	3
Seasonal Index	0.9	X	0.7

The value of x is:

1. 1.6
2. 1.5
3. 1.4

Answer 1

Seasonal indices have an average value of 1. This means that sum of seasonal indices divided by the number of indices should be 1.

This is so because the seasonal indices are measured relative to yearly or overall average or seasonal average. For example, A seasonal index of 1.5 (or 150%) would indicate that the season had 50% more than the seasonal average. Similarly, a seasonal index of 0.9 means that the season had 10% less than the seasonal average.

Now, coming to this problem,

The average of all three trimester seasonal indices should be 1.

So, (0.9 + x + 0.7 ) / 3 = 1

Solving, 1.6 + x = 3

Which gives x = 1.4

So, seasonal index of second trimester should be 1.4

Hence, correct option is C.