University of Bristol
Wellcome Trust
Recommended by:
Society of Biology
PEEP for Physics & Ethics at GCSE

Fractions, Percentages and Expressing Risks

Success or Failure?

Fractions or percentages can also be used to indicate success rates.

Nearly 80 percent - that’s 4/5 - or 4 in every 5 - of multiple sclerosis and spinal cord patients enrolled in British research trials obtained clinical benefit from marijuana extracts, according to data presented at the 2001 meeting of the American Academy of Pain Management by Geoffrey Guy, the Chairman of GW Pharmaceuticals, a London company licensed to cultivate and test medical marijuana in clinical trials.

Remember that a success rate of one in ten equates to a failure rate of 90%. Dolly the sheep, heralded as a success - the first cloned animal to be born - was one in 276 tries.

What is the team who cloned Dolly’s failure rate expressed as a percentage?

  • Show Answer
    • Answer = 99.6%


In 2002-2003 Dr Kuliev and colleagues at the Reproductive Genetics Institute in Chicago treated nine couples with children needing bone marrow transplants. They created 199 embryos using IVF of which 45 were selected as being suitable donors. A total of 28 embryos were transferred to the women in IVF cycles, resulting in five pregnancies and births.


Which is incorrect?
Their success rate was 2.5%.
Their success rate was nearly 18%.
The chance of a couple getting pregnant was slightly less than 1 in 2.
I don’t know, these numbers are too confusing.

 Very Big and Small Numbers

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