How much storage should be allocated for the replication

Hi,

Could please explain me how to calculate following. We know the answer but don't know hoe to calculte it.

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An application uses ten 10 GB Devices. A pointer based replica of the application is required. The replica will be kept for 24 hours. The data changes by 20% every 24 hours. How much storage should be allocated for the replication?

Answer:-  20 GB

An application uses ten 20 GB devices. A full volume replica of the application is required. The replica will be kept for 24 hours and the data changes by 20% every 24 hours. How much storage should be allocated for the replication?

Answer:- 40 GB

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An application uses ten 9 GB devices. A full volume local replica of the application is required every 6 hours. Each replica will be kept for 24 hours. How many replica devices are required?

Answer:- 40

An application uses ten 9 GB Devices. A pointer based replica of the application is required every 4 hours. Each replica will be kept for 24 hours. The data changes by 10% every 4 hours.How many replica devices are required?

Answer:- 60

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Regards,