difference between elastic and scalable expenditure model

I am going through exam questions, where in I find some questions are quite tricky. Where in I got a question in mind, what is difference between elastic and scaleble expenditure model?

The question arrived due to below two questions. Your company is planning to migrate all their virtual machines to an Azure pay-as-you-go subscription. The virtual machines are currently hosted on the Hyper-V hosts in a data center. You are required make sure that the intended Azure solution uses the correct expenditure model. Solution: You should recommend the use of the elastic expenditure model. Does the solution meet the goal? • A. Yes B . No Ans ; No ( B) B is the correct answer. The correct expenditure model is "Operational".

Your company is planning to migrate all their virtual machines to an Azure pay-as-you-go subscription. The virtual machines are currently hosted on the Hyper-V hosts in a data center. You are required make sure that the intended Azure solution uses the correct expenditure model. Solution: You should recommend the use of the scalable expenditure model. Does the solution meet the goal? A. Yes B . No Ans : No(B)

so how to differentiate scalable and operational?

Solution

Scalability is simply an increase in size or number—and, therefore, Elastic is also a form of scaling, but in this case within the same machine.

For example, we have two types of scaling:

HORIZONTAL SCALING (known as Elastic model): Increase memory and storage (etc.) of a VM as the workload increases and reduces accordingly.
VERTICAL SCALING (scalable expenditure model): Increase by adding or attaching more virtual machines of the same size and configuration.

Note: Memory and storage of the same VM are increased IN Elastic models WHILE new VMs are added in SCALABLE MODELS. Either way, just know that the number of VMs remain the same, but memory/storage increases in the 'elastic model' and number of VMs increases as well as memory/storage.