Receivables management

In the e.g 1 on page no. 31 ..in the lecture we have solved with the technique of calculating loss on discount with a interest figure which is 27 % and our overdraft rate is 20% therefore discount should not be given.
Can we solve this e.g by second technique ..this will give same conclusion , i have done it if u can check if its right..

Calculation
1. Cost of discount = 4% of 12m = 480000
2. Savings =
Avg receivables before discount= 3 × 12m / 12 = 3M
Avg receivables after discount = 1 × 12M / 12 $ 1M
Therefore 2M (3-1) can be used to pay overdraft which will save = 2m × 20% = 400000.
3. Net loss = 480000- 400000= 80000
Therefore discount should not be given.

Thanks