“Where are they all coming from?” asked the first.

“Facebook, mainly,” said the second. “Usually with a slick video showing how to multiply 321 by 13 using only a few diagonal lines.”

“Gah,” said the second.

A few hollow voices chanted “4 1 7 3”.

“It’s not that it’s a wrong method,” said the first, preparing the shotgun. “It’s even quite nice as a way of showing where the different bits of, say, the grid method come from.”

“But?” said the second, handing over the ammunition.

“But it relies on counting crossings, and knowing what to do when there’s a carry.” Ker-click.

“So as soon as you do anything with digits bigger than 3, you’ve got problems?” said the second.

“Yup,” said the first, pulling the trigger and sending 978 × 74 towards the nearest zombie.

Its head exploded.

“We’ve got a number system and algorithms that use it for a reason,” he said, holding his hand out for more ammunition. “Let’s show these brainless hordes who’s boss.”