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Either paper 2 marks
A spinner can land on red, blue, green or yellow.
The table gives the probability of each colour.
Colour Red Blue Green Yellow Probability \(0.35\) \(0.15\) \(0.1\) ? Work out the probability that the spinner lands on yellow.
Show answer
\(0.4\)The spinner must land on one of the four colours, so the four probabilities add up to 1.
\(0.35 + 0.15 + 0.1 = 0.6\)
\(1 - 0.6 = 0.4\)
So the probability of yellow is 0.4.
- M1adds the three probabilities, \(0.6\), or subtracts from 1
- A1probability \(0.4\)
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Either paper 4 marks
A game is played 60 times. The chart shows the winning score each time.
(a)Write down the mode of the winning scores.
(b)The game is played again. Use the chart to estimate the probability that the winning score is 26.
(c)Use the chart to estimate the probability that the winning score is 24 or more.
Show answer
(a) \(24\)
(b) \(\frac{ 7 }{ 60 }\)
(c) \(\frac{ 37 }{ 60 }\)The mode is the score with the tallest bar, which is 24.
The bar for 26 has height 7, so the score was 26 in 7 of the 60 games.
So the estimated probability is \(\frac{ 7 }{ 60 }\).
The bars for 24 and every higher score have heights \(16,\ 14,\ 7\), which add up to 37.
So the winning score was 24 or more in 37 of the 60 games.
So the estimated probability is \(\frac{ 37 }{ 60 }\).
- (c) M1adds the bars from 24 upwards to get 37
- (c) A1divides by 60 to get \(\frac{ 37 }{ 60 }\)
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Either paper 3 marks
Here is a fair ordinary dice and a fair spinner. Every section of the spinner is the same size.
In one turn of a game, Anya throws the dice once and spins the spinner once.
Is Anya more likely to get a number less than 2 on the dice or a number greater than 5 on the spinner?
You must show all your working.
Show answer
The dice: dice \(\frac{ 1 }{ 6 } = \frac{ 3 }{ 18 }\), spinner \(\frac{ 1 }{ 9 } = \frac{ 2 }{ 18 }\)The dice has 6 equally likely faces, and 1 of them shows a number less than 2.
\(P(\text{dice less than 2}) = \frac{ 1 }{ 6 }\)
On the spinner there are 9 equal sections. Counting the sections whose number is greater than 5 gives 1.
\(P(\text{spinner greater than 5}) = \frac{ 1 }{ 9 }\)
To compare, write both fractions with denominator 18:
\(\frac{ 1 }{ 6 } = \frac{ 3 }{ 18 }\) and \(\frac{ 1 }{ 9 } = \frac{ 2 }{ 18 }\)
\(\frac{ 3 }{ 18 } > \frac{ 2 }{ 18 }\), so Anya is more likely to succeed on the dice.
- M1P(dice less than 2) \(= \frac{ 1 }{ 6 }\)
- M1P(spinner greater than 5) \(= \frac{ 1 }{ 9 }\), counting 1 of the 9 sections
- A1the dice, comparing \(\frac{ 3 }{ 18 }\) with \(\frac{ 2 }{ 18 }\)
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Either paper 3 marks
A bag contains 12 counters. 3 of the counters are black.
One counter is taken from the bag at random.
(a)Work out the probability that the counter is black. Give your answer as a fraction in its simplest form.
(b)Work out the probability that the counter is not black.
Show answer
(a) \(\frac{1}{4}\)
(b) \(\frac{3}{4}\)3 of the 12 counters are black, so the probability is
\(\frac{ 3 }{ 12 } = \frac{ 1 }{ 4 }\)
The counter is either black or it is not, so the two probabilities add up to 1.
\(1 - \frac{ 1 }{ 4 } = \frac{ 3 }{ 4 }\)
Counting instead gives the same answer: \(12 - 3 = 9\) counters are not black, and \(\frac{ 9 }{ 12 } = \frac{ 3 }{ 4 }\)
- (a) M1fraction \(\frac{ 3 }{ 12 }\)
- (a) A1simplified to \(\frac{ 1 }{ 4 }\)
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Either paper 3 marks
A bag contains counters. Some are purple and the rest are orange.
The probability that a counter taken at random is purple is \(\frac{ 1 }{ 4 }\).
There are 5 counters that are purple.
(a)Calculate how many counters there are altogether.
(b)Calculate how many counters are orange.
Show answer
(a) \(20\)
(b) \(15\)\(\frac{ 1 }{ 4 }\) of the counters are purple, and that is 5 counters.
So one \(\frac{1}{ 4 }\) of the bag is \(5 \div 1 = 5\) counters, and the whole bag is
\(4 \times 5 = 20\)
\(20 - 5 = 15\)
- (a) M1one share of the bag, \(5 \div 1 = 5\)
- (a) A1total \(20\)
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Either paper 3 marksA spinner can land on yellow, green or red only. Priya writes down these probabilities.
Colour Probability yellow 0.3 green 0.4 red 0.4 (a)Explain how you can tell that Priya has made a mistake.
(b)By how much is the total of Priya's probabilities wrong?
Show answer
(a) The three probabilities add to \(1.1\), and the probabilities of all the outcomes must add to exactly 1.
(b) \(0.1\)Add the three probabilities:
\(0.3 + 0.4 + 0.4 = 1.1\)
The spinner must land on one of the three, so the probabilities have to add to exactly 1. \(1.1\) is more than 1, so at least one of them is wrong.
\(1.1 - 1 = 0.1\)
- (a) M1adds the three probabilities to get \(1.1\)
- (a) C1states the total is more than 1 but must be exactly 1
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Either paper 2 marks
A bag contains counters that are yellow, green, red or blue.
One counter is taken at random.
The probability that it is yellow is \(0.3\).
The probability that it is green is \(0.25\).
(a)Calculate the probability that the counter is yellow or green.
(b)Calculate the probability that the counter is neither yellow nor green.
Show answer
(a) \(0.55\)
(b) \(0.45\)A counter cannot be two colours at once, so the two probabilities simply add:
\(0.3 + 0.25 = 0.55\)
Either it is one of those two colours or it is not, and the two probabilities add to 1.
\(1 - 0.55 = 0.45\)
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Either paper 3 marks
A fair spinner is numbered 1 to 5. It is spun once.
A bag contains counters in three colours: blue, purple and orange.
The table shows the probability of taking each colour, except one.
Colour Blue Purple Orange Probability \(0.35\) \(0.35\) ? (a)Find the probability that a counter taken at random from the bag is orange.
(b)Find the probability that the spinner lands on a number greater than 2.
(c)Decide which is more likely: spinning a number greater than 2 on the spinner, or picking an orange counter from the bag.
Give a reason for your answer.
Show answer
(a) \(0.3\)
(b) \(0.6\)
(c) The spinner, because \(0.6\) > \(0.3\)The three probabilities add up to 1.
\(0.35 + 0.35 = 0.7\)
\(1 - 0.7 = 0.3\)
There are 3 numbers greater than 2, out of 5 altogether.
\(\frac{ 3 }{ 5 } = 0.6\)
\(0.6\) (the spinner) compared with \(0.3\) (an orange counter):
\(0.6 > 0.3\), so the spinner is more likely.
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Either paper 3 marks
A fair spinner has 12 equal sections.
Label each section A, B, C or D so that when the arrow is spun: the probability it lands on B is \(\frac{ 1 }{ 6 }\); the probability it lands on C is equal to the probability it lands on D; the probability it lands on A is three times the probability it lands on B.
Show answer
B: 2, C: 2, D: 2, A: 6 (12 sections in total; any arrangement of the sections is accepted)The probability of B is \(\frac{ 1 }{ 6 }\), so out of 12 sections B gets
\(\frac{ 1 }{ 6 } \times 12 = 2\)
The probability of A is three times the probability of B, so A gets
\(3 \times 2 = 6\)
That leaves \(12 - 2 - 6 = 4\) sections for C and D, and their probabilities must be equal, so each gets
\(4 \div 2 = 2\)
So B: 2, C: 2, D: 2, A: 6 — the sections can be arranged in any order around the spinner.
- M1B gets \(\frac{ 1 }{ 6 }\) of 12 sections, so 2
- M1A gets three times B's count, so 6
- A1the 4 sections left are split evenly: C gets 2 and D gets 2
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Either paper 3 marks
A fair, ordinary dice is rolled and a counter is taken at random from a bag.
The tree diagram shows the probabilities.
(a)How do the probabilities show that all the counters in the bag are red, blue or yellow?
(b)Write down the probability that the counter is red or yellow.
(c)Write down the probability that the dice lands on an even number and the counter is red.
Show answer
(a) The three probabilities from each counter node add up to 1: \(\frac{ 6 }{ 25 } + \frac{ 12 }{ 25 } + \frac{ 7 }{ 25 } = 1\), so no other colour is possible.
(b) \(\frac{13}{25}\)
(c) \(\frac{3}{25}\)Each counter node has three branches, and the probabilities on them must cover every possible outcome.
\(\frac{ 6 }{ 25 } + \frac{ 12 }{ 25 } + \frac{ 7 }{ 25 } = \frac{ 25 }{ 25 } = 1\)
The probabilities add up to 1, so there is no probability left for any other colour: every counter is red, blue or yellow.
The counter is red or yellow, so add the two branch probabilities:
\(\frac{ 6 }{ 25 } + \frac{ 7 }{ 25 } = \frac{13}{25}\)
Follow the path Even, then red, and multiply the probabilities along it:
\(\frac{1}{ 2 } \times \frac{ 6 }{ 25 } = \frac{3}{25}\)