It takes five hours for the master to complete a batch of elementary school math problems, and seven hours for the apprentice. Now master and apprentice have been working for two hours, and there are still 198 questions left. Apprentices complete within the cooperation time. Total hours of master completion.

1 ÷ 5 = 1 in 5。

Total hours completed by apprentices.

1 ÷ 7 = 1 in 7。

Master and apprentice work together for 2 hours to complete the total

(0 of 65438+5+0 of 65438+7) × 2 = 24 of 35.

The total number of parts is

198 ÷ (0-24 of 65438+35) = 630 (piece)

The apprentice did it.

630× (1× 2 inch 7) = 180 (piece)