The Boy Loved by Mathematics (5)

"Teacher, what happened?"
"Yes. Keita is working enthusiastically on Japanese, social studies, science, music, and art. I have only been observing him for a month, so this may not be entirely accurate, but other than arithmetic, he is a very normal elementary school student."
"Arithmetic, huh? He's probably not listening in class, just drawing shapes and writing numbers in his notebook, right?"
"That's right, we bought him those triangle rulers, and that's how this all started!"
"Now, now, both father and mother, please listen to me until the end. He's been using triangle rulers since he was in nursery school... I'm starting to understand a little."
"And then..."
"Yes. Let me get to the main point. Actually, I was teaching addition during arithmetic class. Many of the children attended kindergartens in the city, so many of them have already learned a fair amount of arithmetic in kindergarten."
"Keita, he's not able to keep up, is he?"
"No, it's quite the opposite. It was a high-level problem for a first-grader, but when I asked, 'What is the sum of all numbers from 1 to 10?', while everyone else was busy repeating addition..."
The father said in a slightly angry tone, "Was Keita the only one playing around!?"
The mother said worriedly, "Was Keita the only one who couldn't keep up?"
They pressed him.
The teacher said, "Please listen until the end (laughs). Keita instantly calculated 1+10=11, multiplied it by 5, and got 55."
Parents: "(Silence..........)"