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Exchange rates in US$ (Tables)

12 Months Ended

Dec. 31, 2020

Foreign exchange rates [abstract]

Summary of principal exchange rate used in preparation of financial statements

The principal exchange rates used in the preparation of the 2020 financial statements were:


			Full-year average									Year-end
			2020			2019			2018			2020			2019			2018
Sterling			1.28			1.28			1.34			1.36			1.31			1.27
Australian dollar			0.69			0.70			0.75			0.77			0.70			0.70
Canadian dollar			0.75			0.75			0.77			0.78			0.77			0.73
Euro			1.14			1.12			1.18			1.23			1.12			1.14
South African rand			0.061			0.069			0.076			0.068			0.071			0.069