Level 7 Probability question.
A bag contains that are red, black, or green.
1/3 of the counters are red. 1/6 of the counters are black.
There are 15 green counters in the bag. How many black counters are in the bag?
Answers
Ok so this is about finding equivalent fractions.
If we know that 1/6 of the counters are black and 1/3 of the counters are red then we can find what proportion of the counters are green by making 1/6 and 1/3 equivalent. To do this we ask what do we have to do to make 3 equal 6? We can multiply it by two. So 1/3 = 2/6.
So if 2/6 are red and 1/6 are black then we know that 3/6 are green (6-2-1=3)
If 3/6 is equivalent to 15 then we have to ask what do we have to do to make 3 equal 15? We multiply it by 5. We know that 1/6 is the proportion of black counters so we multiply 1x5 = 5. There are 5 black counters.
16 February 2011
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