Festive fireplace


Another photo of our Christmas decorations, this time our festive fireplace. Let’s just pray that it doesn’t go up in flames this year.

Not that it’s ever gone up in flames, but it’s a good thing to wish for, none-the-less.

You may notice that one of the ‘Christmas tree’ bulbs wound around the greenery is green (right-hand top corner of the mantlepiece). This replaced a bulb that had blown. Rather than using the ye olde tried-and-tested method of systematically replacing each and every bulb until you get to the one that’s gone I went to my toolbox and got out my pen-like voltage detector. (below)

A red, pen-like electrical-signal scanner.
My red, pen-like MK live-wire detector. Bought at B&Q, in exchange for money.

This is a small, handheld device that is usually used to check for electrical signals behind walls, bleeping and flashing when it detects an AC current. It occured to me that this might also work in detecting where the circuit was broken on these Christmas tree lights.

I started scanning at the plug end and followed the wire up and along the mantlepiece. Beep, beep, beep, beep, beep, beep, then nothing! I replaced the bulb at the point that the beeping had stopped and hey presto! (or any other 1980s UK supermarket chain) the lights worked.

My little festive tip for you all there.

Rapidly square any number ending in 5

Book cover for Rapid Math Tricks and TipsA couple of days ago I blogged about this book: Rapid Math Tricks and Tips: 30 Days to Number Power by Edward H. Julius (Wiley, 1992) ISBN 0-471-57563-1. I’ve had quite a few people saying how fun that last tip was (multiplying by 99). Here’s my favourite trick of all in the first book: how to square any number that ends in 5. (Remember that the symbol (^) means raise to the power, so 5^2 is 5 raised to the power of 2, or 5 x 5.)

Here’s what Edward H. Julius has to say:

Strategy: This trick is one of the oldest in the book, and one of the best! To square a number that ends in 5,

  1. first multiply the tens digit by the next whole number.
  2. To that product, affix the number 25.

The number to affix (25) is easy to remember, because 5^2 = 25. Although a calculation such as 7.5 x 750 is technically not a square, it too can be solved using this technique. This trick will also work for numbers with more than two digits.

For example: 15^2:

  1. Multiply the tens digit (1) by the next whole number (2): 1 x 2 = 2.
  2. Affix 25 to that answer: 225 (the answer).

Another example, 65^2:

  1. Multiply 6 x 7 = 42
  2. Affix 25: 4,225 (the answer)

How about, 450^2:

  1. Ignore the zero and think 45^2
  2. Multiply 4 x 5 = 20
  3. Affix 25: 2025
  4. For each zero initially disregarded in a squaring problem two must eventually be affixed to obtain the product.
  5. Affird two zeros to the end: 202,500.

And what about the not-squared problem? This method only works if the two numbers have the same digits, eg 65 x 6.5 or 950 x 9.5 but not 65 x 3.5. So for 65 x 6.5:

  1. Disregard the decimal point for now
  2. Multiply 6 x 7 = 42
  3. Affix 25: 4225
  4. Applying a test of reasonableness you can see that 65 x 5 would be 325, so x 6.5 must be between 325 and 650 (which is 65 x 10). So re-inserting the decimal point gives the answer: 422.5.

How cool is that! Now, go buy the book! It’s only £6.96 at Amazon UK.

I can now multiply quickly by 99

Book cover for Rapid Math Tricks and TipsLast night I was making some space on my shelves for a couple of books on PHP and MySQL that I’d got back from my friend Mike when I came across this book: Rapid Math Tricks and Tips: 30 Days to Number Power by Edward H. Julius (Wiley, 1992) ISBN 0-471-57563-1.

I’ve always loved maths; maybe something to do with Dad having been a draughtsman and electrical engineer. At high school the only Certificate of Sixth Year Studies (CSYS) I took was in Maths, Paper II: Calculus. I really wish that I’d had this book while I was at school. It’s brilliant!

The book is a 30-day self-teaching guide designed to help you master common maths problems without a calculator. It uses tips and techniques to teach the basics of multiplication, division, subtraction and addition as well as estimation and more advanced techniques.

Last night I learned in less than five minutes how to “Rapidly multiply any one- or two-digit number by 99 (or 0.99, 0.0, 990, etc.)”. Here’s how:

  1. Subtract 1 from the number to obtain the left-hand portion of the answer
  2. Then subtract the number from 100 to obtain the right-hand portion

For example, 15 x 99:

  1. Subtract: 15 – 1 = 14 (left-hand portion of the answer)
  2. Subtract: 100 – 15 = 85 (right-hand portion of the answer)
  3. Combine: 1,485 is the answer

Another example, 430 x 0.99:

  1. Disregard the zero and decimal point, and subtract: 43 – 1 – 42 (left-hand portion of the answer)
  2. Subtract: 100 – 43 = 57 (right-hand portion of the answer)
  3. Combine: 4,257 (intermediary product)
  4. Apply Test of Reasonableness: 0.99 is almost 1, so 430 x 0.99 must equal just under 430. Insert a decimal point within the intermediary product to obtain the answer, 425.7.

How cool is that!

How to clean cat pee from a guitar amp

Laney GC80A in the midst of being cleaned

On Thursday I have a rehearsal for a monthly youth event called Powerpoint, which is now being overseen by SU Scotland. The next Powerpoint is on Friday evening from 19:30.

Imagine my dismay the other evening when I got my guitars and amps out to check them over to discover that one (or more) of our cats have pee-ed on my Laney GC80A amp. This afternoon I carefully removed the front kick-grille and washed it and the cabinet down with Simple Solution’s Cat Spray & Urine Stain & Odor Remover.

What a marvellous liquid! For years I’ve been looking (obviously not hard enough) for something that effectively deals with cat stains, and now I’ve found it. I’ve already used it on a carpet, my wardrobe doors(!), and now my guitar amp.

The science bit: Cat urine is made up of three parts:

  1. urea, which is the sticky part,
  2. urochrome, which is the pigment or colour part, and
  3. uric acid crystals and salts, which is the er… salty, crystally part.

Seemingly a lot of products will work on the first two parts but not the third, and the crystals and salts just dry and become dormant. But as soon as the area gets wet again the smell returns. Simple Solution’s Cat Spray and Urine Stain and Odor Remover is biological and works on all three parts. And do you know what? It really does work. It’s great.

Now I can be certain that the only thing that will stink on Friday night is my playing!