The photograph shows kenaf plants that grow in many African countries. (Source: © Dorling Kindersley Ltd / Alamy Stock Photo) The plants are grown for food and as a source of fibres. A scientist investigated the tensile strength of samples of fibres from kenaf plants. Some of the samples of fibres were treated with hydrogen peroxide and other samples were untreated. The force needed to break each fibre was measured. The diagram shows the apparatus used. The apparatus shows a force meter that pulls on the attached fibre. The force needed to break the fibre is recorded on the computer. The table shows the results of this investigation. Calculate the mean percentage increase in tensile strength of fibres treated with hydrogen peroxide compared to untreated fibres. Give your answer to three significant figures. (3) .......................................................... ..

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