Penguin Random House contributed 24 million pounds in operating profit to Pearson in the first half of 2015, up from 18 million pounds in the same period in 2014.

Pearson, which owns a 47% stake in PRH, attributed the increase in profit contribution to “multi-geographic adult bestsellers” including The Girl on the Train and Grey, which sold 4 million and 3 million copies, respectively, in the first six months of 2015.

The company’s children’s publishing program also had a strong showing in the period with Pearson pointing to books by authors John Green, Dr. Seuss and James Dashner as selling very well in the first half of the year.

Earnings have also been helped by a smooth integration process. Pearson noted that system integration and warehouse consolidation in the U.S. was completed in the first half of the year and good progress has been made in the U.K. and Australia.

Bertelsmann, which owns 53% of PRH, will issue a more detailed report on PRH results in late August.