# Top four maths mistakes

Maths is fun, right? For some, yes, but for others it’s a finger-counting nightmare. Colin Marrs puts the calculator away and shows you four classic maths mistakes most people make

As many an accountant will tell you, maths is fun. Or is it?

A major Government survey released in 2011 revealed that 17m adults in England possess numeracy skills no better than those expected of children at the end of primary school.

By comparison, the number of adults whose literacy is at the equivalent level is just five million. There can be no doubt – of the three Rs, it is the arithmetic that most really struggle with, with some arguing modern technology only compounds the problem.

Think you’re a maths whizz? Here are four common maths blunders that most get wrong:

1. Black cloud

Forecasters have been known to say that because there is a 50% chance of rain on Saturday and 50% chance on Sunday, there is a 100% chance of rain at the weekend. This is false. In fact, there is a 25% chance you won’t see a drop of rain all weekend.

2. Birthday bumps

If you ask most people the chances of two people in a class of 40 people sharing the same birthday, many people would assume that the figure should be around 10%.

They may also assume that the chances of a match don’t get near 100% until there are 366 people in the room (the number of days in a year plus one).

However, in reality, 99% probability of a share is reached with just 57 people. Each individual person has only a small chance of finding a match, but each person is trying it 56 times, increasing the probability dramatically.

3. Killing time

The division of the day into 24 hours of 60 minutes still causes confusion, apparently. Many people often mistakenly calculate 3.1 hours as three hours 10 minutes, which would mean 6.7 hours was actually 7 hours 10 minutes. Got it?

4. Percentage points

Newspapers and TV stations often get into a muddle when dealing with percentages. Opinion polls might show that a political party has a 40% share of the vote and another has 30%.

If the first party’s share drops to 35%, but the second party remains steady at 30%, the lead might be incorrectly described as having been cut by five per cent. Others might – correctly – describe the lead as having been halved.

Help at hand with AAT Essentials

AAT runs a range of courses that have been developed for businesspeople without an accounting and finance background. For more details of the courses, call 020 7397 3000, email or visit the AAT website.

Colin Marrs is an independent writing and editing professional.