Joint costing

Hello sir,

If sales – 2000 , production – 4000 and sales price is 10/unit – A
If sales – 2000 , production – 2000 and sales price is 12 /unit – B
with a joint cost of 10000 what is the total profit on the basis of units produced basis ?

Cost / unit = 10000/ 6000= 1.67

Therefore

Profit of A – 20000 – 6680 = 13320
Profit of B – 24000 – 3340= 20660

This if done on the basis of sales value of production

Cost of A = 40000/64000 X 10000 = 6250
Cost of B = 24000/64000 X 10000= 3750

Profit = 20000 – 6250 = 13750
profit of B = 240000 -3750 = 20250

But i read somewhere that irrespective of the method total profits should be same which is not the case here. Can you explain why