‘Per cent’ literally means ‘out of each hundred’. So if we could divide up the whole into 100 parts, 10% would represent 10 out of the 100 parts, 25% would be 25 parts, and 50%.

Notice that taking 50% is just the same as taking half of something. It is also true that taking 25% is like taking a quarter, 20% is a fifth, and 10% is a tenth.

Mortgages are advertised at the following rates. Which of these banks/building societies give the best rate?

Alliance & Chester | 12.5% | Royal Bank of Wales | 5.5% |

Alternative Life | 8.3% | Southern Rock | 23.7% |

Lancashire Building Society | 7.6% | Uncooperative Bank | 19.2% |

The Royal Bank of Wales gives the lowest interest rate, and so this would be the best choice.

On a carton of Tropical Fruit Juice, the carton states that the contents are as given below. What is wrong with this statement?

Orange Juice | Pineapple Juice | Mango Extract | Papaya Extract |
---|---|---|---|

40% | 30% | 25% | 15% |

These percentage values should add up to 100%, but they add up to 110%, which is not possible.

The shoe shop in the high street is closing down, so I pop in to see if I can find a bargain. All shoes are being sold at 50% off the marked price. I find a really nice pair of shoes priced at £60. How much would it cost to treat myself to this pair of shoes?

SolutionThe original price can be thought of as the full 100%, and we need to find the discount price.

So, how much is the price reduced by? The discount is 50%, or 50 parts out of 100 of the original price. Where we read the word *of *we can replace this with *multiplied by*, and write

So the shoes are being sold at £30 off the original price, which leaves £30 to pay.

You may have known straight away that ‘50% off’ is the same as saying ‘half price’, and you’d have been able to work out immediately that half of £60 is £30.

To know the real value of a percentage, we need to know what it is a percentage of. For instance, in our shoe shop in Example 3, all shoes are 50% off. For a £60 pair of shoes this means £30 off, but if I had chosen a £20 pair of shoes the reduction would be only £10.

The pass mark for an exam is 60%, and there are 40 questions on the exam sheet. How many questions do I need to get right in order to pass the exam?

SolutionIf I got all the questions correct, I would score 100%. Fortunately, I only need to get 60%, or 60 out of every hundred of the questions correct. There are only 40 questions, so let’s take sixty hundredths of these 40 questions.

So 24 out of 40 questions corresponds to 60%, and as long as I can answer at least 24 questions correctly I will pass the exam.

To express one quantity as a percentage of another, we must first express this as a proportion, and then convert this to a percentage by multiplying by 100.

In an exam I managed to answer 18 questions correctly out of a total of 30. What is my score as a percentage?

SolutionIn this question we are being asked to convert to a percentage. If 100% represents the whole, or in this case, the total number of questions, we are asking how many parts out of 100 would we have? In other words, how many parts out of 100 does 18 out of 30 correspond to?

To do this, we take our proportion and times by 100

So I have scored 60% on this exam.

My tin of Apples and Pears is 35% apple and 40% syrup. What percentage of it is pear?

The brand of teabags I normally buy have a special offer on. The offer is 25% Extra Free. I normally buy a packet of 48 teabags. How many teabags will I get in my packet this time?

The pass mark for an exam is 40%, and there are 25 questions on the exam sheet. How many questions do I need to get right in order to pass the exam?

Radio alarm clocks were selling at £25 but have been reduced to £20. What percentage reduction does this represent on the original price?

Which is the greatest, 25% of 32 or 20% of 35 or 15% of 40?

I have £5,000 in a building society account with an interest rate of 4.1% per annum. How much interest will I earn at the end of the year?

Over the course of a year Jake gets the following marks in his exams. Which is Jake’s best subject?

Accounting & Finance | Algebra | Trigonometry | Calculus |
---|---|---|---|

47 out of 80 | 39 out of 70 | 32 out of 40 | 41 out of 50 |

Tickets for the Comedy Club cost £12 on the door. There is a 15% discount when booking in advance over the internet. How much will my ticket cost if I book on-line?