Probability of jelly babies

Difficulty:
intermediate

Rating:
4-stars

GCSE Marks:
4-marks

GCSE Text:
Hayley receives a tub of sweets for her birthday, containing a total of 70 coloured sweets. She counts them and find that there are 28 red sweets, 7 orange, 13 yellow and 9 black sweets. The rest are green.

a) For each colour, calculate the probability that a sweet of that colour would be chosen if a sweet was picked at random.

A super-tub of the same sweets can be bought which contains 350 sweets in total.

b) If the probabilities of the sweets in the super-tub are the same as in Hayley’s tub, how many red sweets would we expect to find in one of the super-tubs?

Suggestions:
Students love questions involving food and sweets, so this video is popular with students. The format of simple probability is very close to a GCSE question that could appear on both a Foundation and Higher paper.

Extension Ideas:
Teachers could extend the learning by considering:

  • If there were 27 red sweets in the birthday tub instead of 28, how would that affect the probability of red sweets, and how would that affect the expected quantity of red sweets in a super-tub?
  • If a sweet is taken at random, and then eaten, then a second sweet is taken at random and eaten, what is the probability that both of those sweets were red? (introducing ‘without replacement’ concepts and tree diagrams to represent the problem).

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