For the five values 12, \( a \), 17, 21, 22, the three years moving averages are 13, 16, 20. The value of \( a \) is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 10
A three-year moving average is the mean of three consecutive values. The first moving average contains a, so
\( \displaystyle \frac{12+a+17}{3}=13 \)
\( \displaystyle 29+a=39 \)
\( \displaystyle a=10 \)
This agrees with the second average, \( \frac{10+17+21}{3}=16 \).