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Exchange rates in US$
 12 Months Ended
Dec. 31, 2019
Foreign exchange rates [abstract]  
Exchange rates in US$
41 Exchange rates in US$
The principal exchange rates used in the preparation of the 2019 financial statements were:

Full-year average
Year-end

2019

2018

2017

2019

2018

2017

Sterling
1.28

1.34

1.29

1.31

1.27

1.34

Australian dollar
0.70

0.75

0.77

0.70

0.70

0.78

Canadian dollar
0.75

0.77

0.77

0.77

0.73

0.79

Euro
1.12

1.18

1.13

1.12

1.14

1.20

South African rand
0.069

0.076

0.075

0.071

0.069

0.081