Jesus answers their reasoning about bread with their own memory. They had only one loaf (Mark 8:14, 16). So He asks them to count what was left over the last time they had too little. Five loaves had fed five thousand men, and there was more left over than they started with.

Gill says that by this question "Their memories were hereby refreshed, and they call to mind the exact number of the baskets of fragments." Matthew Henry captures the point Jesus was making: "As if he that multiplied five loaves, and seven, could not multiply one."

"They say unto him, Twelve" (Mark 8:19). The disciples remember the number exactly, matching Mark's earlier account: "they took up twelve baskets full of the fragments, and of the fishes" (Mark 6:43). Jesus then asks the same about the seven loaves, and they answer, "Seven" (Mark 8:20). Their memory was sound, which is why He presses one more question: "How is it that ye do not understand?" (Mark 8:21).

The basket named here is the kophinos, which Thayer defines as "a basket, wicker basket." In the New Testament this word appears only in the accounts of the feeding of the five thousand and in Jesus' reminders about it (Matthew 14:20; Mark 6:43; Luke 9:17; John 6:13; Matthew 16:9; Mark 8:19). When Jesus asks about the four thousand in Mark 8:20, a different word is used, spuris. Mark keeps the two baskets distinct even in Jesus' questions.

The "fragments" (klasma) are broken pieces, the bread Jesus had broken and given out.

This question shows how Jesus teaches faith. He does not simply tell the disciples to stop worrying. He makes them say the number out loud. The evidence for trusting Him was already in their own hands, twelve baskets of it.

The question also shows something about God's provision. In Mark 6:41-44 Jesus did not just give enough. He gave so much that there were baskets left over. Henry notes that for the Lord it is "as easy to make one loaf to feed five thousand as five." The disciples' one loaf in the ship was never the real problem.