Posts Tagged ‘cost’


Awesome Lego Maths and a Giant Lego Tree

July 28, 2018

You may not want Lego brick blossoms falling on your head,

but the Giant Lego Cherry Blossom tree has some awesome maths

to explore. See the tree built in fast forward below.


Hair Maths 4: The Great SHAMPOO rip off

April 27, 2015

According to

There are two types of ingredients in shampoo. One type cleans your hair. The other type strokes your emotions.

Hair Maths Mathspig

Shampoo has one main ingredient:


The two most common shampoo detergents are ammonium lauryl sulphate and ammonium laureth sulphate. That’s all you need to clean your hair. All those shampoo bottles. All that supermarket shelf space offer THE SAME PRODUCT.

Mathspig Colin Farrell shampoo

Other ingredients include: perfume, dye, preservative, foaming agent, acid (The problem is hair swells in an alkaline solution eg with soap when rinsed out the hair shrinks making knots impossible to brush out. ARggghhhhh!), thickeners, thinners, sheen additive, pearlesence powder (makes shampoo look pearly) etc

According to Steve Antczak, Co-author of Cosmetics Unmasked: Your family guide to safe cosmetics and allergy-free toiletries,

A typical shampoo is mostly water, containing between 5 and 20 per cent detergent, with shampoo for dry hair containing less detergent than shampoo for greasy hair.

See New Scientist, Sept , 2009

So the potency of shampoo looks something like this: 

Mathspig % detergent in some shampoos 1

Assume you buy a 500ml bottle of shampoo for $10. Now you can work out how much some shampoo manufacturers rip you off by filling in this table:

Mathspig % detergent in shampoo Q

How much do you pay for water in shampoo? The Answer is here. Mathspig % detergent in shampoo ANS 

What does Bill Bunn from recommend?

My new shampoo, Sunlight Dish Detergent, has just four ingredients. It’s runny and slightly acidic, smells vaguely lemony, doesn’t foam excessively and looks anemic.


Maths Mystery Box 7: PHONES

February 18, 2015

Maths Mystery BOX 7

Middle school maths challenge

Algebra & texting

or  LGbra & txtN

According to a Nielsen Survey the Average US teen sends 3,000 txt messages a month. Averages don’t tell us very much. As this fab post at Maths PLUS explains. The average number of ears on 5 people is 1.8 if one dude has one ear. The Nielsen study did show the averages by gender. Mathspig texting 1 Mathspig texting 2 Mathspig texting 3

This is the maximum cost per txt for pre-paid phone cards. Anyone who sends this many txt messages a month would be crazy if they didn’t use a monthly phone plan.Mathspig texting 4 Mathspig texting 5


Mathspig texting 6

Some txts are serious. Very serious.

The 24/7 CRISIS TEXT LINE in the USA has helped many teenagers in crisis.

The phone no. in the USA is


the numbers down the Left of the phone.

OR from outside USA add code here. You can find details of the Crisis TEXT LINE in R U There? By Alice Gregory, The New Yorker (9 FEB 2015)


Ha Ha!

Some txts are NOT serious.

Texting Boredom Mathspig 7

Would you pay for this?

Mathspig texting  8