Volume Weighted average

Let’s say we have the Triangle

AY	12m	24m	36m	48m
2019	102	135	161	160
2020	100	120	153
2021	108	153
2022	110
To find the volume-weighted development factor 12-24 month maturity, we use

$$\frac{135+120+153}{102+100+108}=1.316$$

We need to use same number of observations while calculating the average