“It doesn’t matter a bit,” she said, removing fragments of shell from her lap; and, to put him at his ease again, went on “Are you interested in little problems at all?”

Herbert, who would have been interested even in a photograph album just then, emerged from his apologies and swore that he was.

“We’re all worrying about one which Father saw in a paper.  I do wish you could solve it for us.  It goes like this.”  And she proceeded to explain it.  Herbert decided that the small piece of meringue still in her hair was not worth mentioning, and he listened to her with interest.

On the next morning I happened to drop in at Herbert’s office....  And that, in short, is how I was entangled in the business.

“Look here,” said Herbert, “you used to be mathematical; here’s something for you.”

“Let the dead past bury its dead,” I implored.  “I am now quite respectable.”

“It goes like this,” he said, ignoring my appeal.

He then gave me the problem, which I hand on to you.

“A subaltern riding at the rear of a column of soldiers trotted up to the captain in front and challenged him to a game of billiards for half a crown a side, the loser to pay for the table.  Having lost, he played another hundred, double or quits, and then rode back, the column by this time having travelled twice its own length, and a distance equal to the distance it would have travelled if it had been going in the other direction.  What was the captain’s name?”

Perhaps I have not got it quite right, for I have had an eventful week since then; or perhaps Herbert didn’t get it quite right; or perhaps the girl with the meringue in her hair didn’t get it quite right; but anyhow, that was the idea of it.

“And the answer,” said Herbert, “ought to be ‘four cows,’ but I keep on making it ‘eight and tuppence.’  Just have a shot at it, there’s a good fellow.  I promised the girl, you know.”

I sat down, worked it out hastily on the back of an envelope, and made it a yard and a half.

“No,” said Herbert; “I know it’s ‘four cows,’ but I can’t get it.”

“Sorry,” I said, “how stupid of me; I left out the table-money.”

I did it hastily again and made it three minutes twenty-five seconds.

“It is difficult, isn’t it?” said Herbert.  “I thought, as you used to be mathematical and as I’d promised the girl—­”

“Wait a moment,” I said, still busy with my envelope.  “I forgot the subaltern.  Ah, that’s right.  The answer is a hundred and twenty-five men....  No, that’s wrong—­I never doubled the half-crown.  Er—­oh, look here, Herbert, I’m rather busy this morning.  I’ll send it to you.”

“Right,” said Herbert.  “I know I can depend on you, because you’re mathematical.”  And he opened the door for me.

I had meant to do a very important piece of work that day, but I couldn’t get my mind off Herbert’s wretched problem.  Happening to see Carey at teatime, I mentioned it to him.