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How Many Gorillas?

Age 14 to 16 Short
Challenge Level


A newspaper article about the wildlife in an African country contains the sentence "The number of gorillas has fallen by 70% in the last 10 years, and there are now only around 5000 left."

If 70% has been given to the nearest 1%, and the number of gorillas left now is correct to the nearest 1000, then what is the largest number of gorillas that there could have been 10 years ago?



This problem is adapted from the World Mathematics Championships
You can find more short problems, arranged by curriculum topic, in our short problems collection.
The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
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