How_To_Be_Good_At_Math

STATISTICS • CALCULATING PROBABILITY 299

Decimals and percentages

Probabilities are most often written as

fractions, but they can also be shown

as decimals or percentages.

Written as a fraction, the probability

is^3 / 12. We can simplify this to^1 / 4. Now

we divide 1 by 4 to find the probability as

a decimal: 1 ÷ 4 = 0.25. To change our

decimal to a percentage, we simply

multiply it by 100. So, 0.25 × 100 = 25%

This box of 12 cakes contains three

chocolate cakes and nine vanilla

cakes. With our eyes shut, we have a 3 in

12 chance of choosing a chocolate cake.

What is the most likely total

to occur when you roll two dice

together? Start by writing down all

the possible scores, and adding the

numbers together.

What are the two least likely

totals to occur?

What are the probabilities

of getting the most likely

and the least likely totals?

Nine chocolate cakes, three vanilla cakes

Three chocolate cakes, nine vanilla cakes

Let’s see what happens if the box

contains nine chocolate cakes and

three vanilla cakes.

Now the probability of picking

a chocolate cake is^9 / 12 , or^3 / 4.

This is the same as 0.75 or 75%.

TRY IT OUT

Answers on page 320

Probability dice

Throwing dice is a great way

to investigate probability. Dice

throws are often important in

board games, so if you know

the probability of certain

combinations occurring, you

might be able to improve

your gameplay!

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