The tallest

The tallest building in the world used to be Taipei 101 in Taiwan. Its height is 0.509 km. The tallest building in North America was Sears Towers in Chicago, USA. Its height is 0.442 km. What is the difference in the heights of the buildings?

Correct answer:

x =  67 m

Step-by-step explanation:

$$\begin{gathered} a=0.509\text{km}\to \text{m}=0.509\cdot 1000\text{m}=509\text{m} \\ b=0.442\text{km}\to \text{m}=0.442\cdot 1000\text{m}=442\text{m} \\ x=a-b=509-442=67\text{m} \end{gathered}$$

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