Specifically: annuity benefit

Why is:

$$10p_{xy} v^{10} \ddot{a}_{\overline{x+10: y+10}}$$insufficient to calculate the EPV?

The memo answer, $${10}p_{xy} v^{10} \ddot{a}_{\overline{x+10: y+10}}+\ddot{a}_{x+10}10p_{x}10q_{y}v^{10} + \ddot{a}_{y+10}10p_{y}10q_{x}v^{10} $$

where x = 60 female, y = 64 male