Alberta NDP Leader Rachel Notley poked fun at one of her United Conservative Party opponents on Tuesday, after he criticized the party’s mathematics policy in a tweet that didn’t quite add up.

“42% has become acceptable as a passing great (sic). Let that sink in,” tweeted Drew Barnes, UCP candidate for Cypress—Medicine Hat. “That means it has become acceptable for children to not know 68% of the material they are taught in school,” he went on.

Notley tweeted back: “Not gonna say it... not gonna say it... not gonna say it,” and then added, “Fine. I’ll say it. Math is hard.”

Her response was a joke that many Albertans will get. The late Progressive Conservative Leader Jim Prentice turned to Notley during a 2015 election debate while discussing her corporate tax rate proposal and said “I know that math is difficult.” He was accused of sexism and later lost the race.

Barnes’ comment was highlighting the fact that Alberta’s standardized Grade 9 math tests only required a score of 42 per cent to be considered a pass in 2017-18. Alberta’s NDP education minister said at the time that the score had changed to account for a more difficult test.

Barnes’ gaffe came just as UCP Leader Jason Kenney was unveiling the party’s education platform. Kenney has vowed to put more emphasis to standardized testing by making diploma exams worth half of secondary students’ final grades, up from the current 30 per cent.

Notley’s NDP hasn’t released an education platform but she has said the party would continue to build and modernize schools and add new funding to hire teachers as populations grow.

Albertans go to the polls on April 16.