I found this qs in "Head First PMP" please see if this is considered as "typical ", can use following formula for the calculation ?

Question 73: Two months ago your customer has formally submitted several
changes to the project. These changes were reviewed and approved by the change
board. Today you are reviewing the first project numbers affected by these
approved changes: EV = 240,000, AC = 260,000, PV = 250,000, SPI = 0.96, BAC =
700,000. How much is your new ETC?

A.) 500,000
B.) 460,000
C.) ETC cannot be calculated and a new bottom up estimate is required
D.) 479,166

There are many ways in which you can calculate the ETC and each is based on
a particular assumption on how the project is progressing. Your interpretation of
the assumptions is required. Here are the formulas:

• ETC = EAC-AC: Use formula when no keywords (i.e. typical, atypical or
flawed) are given.
• ETC = BAC-EV: Assumption: use formula if current variances are thought
to be atypical in the future.
• ETC = (BAC-EV) / CPI: Assumption: use formula if current variances are
thought to be typical in the future.
• ETC = New estimate when it is thought that the original estimate was
flawed.

In this question, the customer has submitted changes. These changes were
approved, implemented and have then caused project variances. Because the
variances are caused by approved changes, we can safely assume that the
variances will continue in the future. As such, the variances can be assumed to be
typical. Therefore, we have to use the 3rd formula in the list above:
ETC = (BAC-EV) / CPI = (700,000 - 240,000) / ???????
At this point you will realize that the CPI is not give in the question, therefore you
first have to calculate it:
CPI = EV / AC = 240,000 / 260,000 = 0.92
Now you can calculate the ETC:
ETC = (BAC-EV) / CPI = (700,000 - 240,000) / 0.92 = 500,000