# October, 2020

## A Catriona Shearer Classic

If you’ve read this blog for a while, you’ll know I’m a fan of @cshearer41’s puzzles (her book, Geometry Puzzles in Felt Tip, is available wherever etc). At a recent MathsJam, one jumped out of Chalkdust at us: (Image from Issue 10 of Chalkdust, a magazine for the mathematically curious.)

## Ask Uncle Colin: how many zeros?

Dear Uncle Colin, How many zeros are there on the end of $100!$? I worked it out to be 21, but the answer sheet says it’s 23 – and my calculator just gives an error message. What do you think? - Maybe A Tutor Has Exact, Reasoned Response? Hi, MATHERR,

## Completing the square

Suppose we have $ax^2 + bx + c = 0$. It’d be easier to complete the square if the $x$ term were even, so let’s double: $2ax^2 + 2bx + 2c = 0$ It’s also be nicer if the $x^2$ term were a square, so let’s multiply by $2a$: \$4a^2x^2

## Ask Uncle Colin: A Pair Of Toy Trucks

Dear Uncle Colin, I have an exam question I don’t understand! There’s a toy truck of mass 5kg attached (by a rod) to another truck of mass 2kg on a slope at 10 degrees to the horizontal. The resistances to motion are 8N and 6N, respectively, and the whole thing

## Dictionary of Mathematical Eponymy: Volder’s algorithm

One of the questions that occasionally crops up in the hive of scum and villainy I hang out in search of problems to solve is, “how do calculators work out trigonometric values?”. It’s not, typically, the way that the Mathematical Ninja would (find an angle nearby and adjust using heuristics),