Pennsylvania Gov. Tom Corbett reached a deal with the Obama administration to extend the state's Medicaid program to half a million low-income residents under the Affordable Care Act, officials said Thursday.

Pennsylvania is now the 27th state to agree to broaden Medicaid to include everyone earning up to a third more than the federal poverty level, or around $16,000 for a single adult. The agreement makes Mr. Corbett, a Republican, the ninth GOP governor to go along with a central part of the 2010 health-care law.

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