Table:
|  | 30 June 2019 | 30 June 2018 |
| --- | --- | --- |
|  | $'000 | $'000 |
| CASH AT BANK |  |  |
| AA rated | 398,999 | 417,982 |
| SECURITY DEPOSITS |  |  |
| AA rated | 8,822 | 4,151 |
Paragraphs:
15 Financial risk management (continued)
(b) Credit risk
Credit risk arises from cash and cash equivalents, and trade and other receivables.
(i) Cash and cash equivalents and security deposits
Deposits are placed with Australian banks or independently rated parties with a minimum rating of ‘BBB+’. To reduce exposure deposits are placed with a variety of financial institutions.
The credit quality of financial assets can be assessed by reference to external credit ratings (if available) or to historical information about counterparty default rates:
In determining the credit quality of these financial assets, NEXTDC has used the long-term rating from Standard & Poor’s as of July 2019.
Question:
What was the average difference between cash at bank and security deposits for both years?
Answer: ((398999 - 8822) + (417982 - 4151)) / 2  = 402004