Checks with https://visualqa.org/download.html:

• Num train questions: 443,757

• Num val questions: 214,354

• Num test questions: 447,793

• Num train answers: 4,437,570

• Num val answers: 2,143,540

• Num train images: 82,783

• Num val images: 40,504

• Num test images: 81,434

testdev is not mentionned:

• Num questions: 107,394
• Num images: 36,807