Washington (CNN) Democrats on the House Financial Services Committee grilled the Consumer Financial Protection Bureau's new chief Kathy Kraninger on Thursday, in her first appearance before Congress since she was appointed in December.

Kraninger was questioned about decisions made under her predecessor, Mick Mulvaney, as well as about the bureau's role in protecting service members and student debtors -- and was at one point asked to calculate the annual percentage rate on a hypothetical payday loan.

Freshman California Rep. Katie Porter posed the math problem and provided the agency chief with a calculator. Porter, a former law professor who brought along the textbook she wrote titled "Modern Consumer Law," also quizzed Kraninger about the definition of an interest rate.

Kraninger declined to answer, responding: "This is not a math exercise."

Democrats are concerned not just that Kraninger may lack the expertise to lead the bureau, but also that she will follow Mulvaney's playbook and scale back enforcement actions. Many Republicans have long argued that the bureau has overstepped its authority and created burdensome standards for businesses.

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