I'm confused about this and I don't wanna take any chances because I know I've seen this in prior exams =(

The "Failure to Pay Penalty": does not apply if (1) at least 90% of the tax is paid in by the unextended due date and (2) the balance of the tax is paid by the extended due date.

ok that makes sense, but then Becker has an explanation to a question as follows:

16,000 withheld from paychecks, filed a timely extension on April 15th and paid an additional $300, filed the tax return by the extended due date and tax liability was $16,500, taxpayer paid the remaining tax on extended due date.

Becker explains that the taxpayer would not have a penalty for underpayment of taxes but that the "failure to pay penalty" would apply on the $200???? how is that so???? at least 90% was paid and the remaining balance was paid by the extended due date =/