The age of the grandfather is twice that of the father, and the age of the father is seven times that of the son. It is known that the age of the grandfather is 70 years old. How old is the son?
爷爷的年龄是爸爸的2倍，爸爸的年龄是儿子的7倍，已知爷爷的年龄是70岁，儿子的年龄是几岁？
<gadget id="calculator">70 / 2 / 7</gadget>
<output>5</output>

<result>5</result>