algebra
posted by Mary .
Let U=1,2,3,4,5,6,7,8,9,10
{xx is multiply of 2} U {x is multiply of 7}

Translating in English,
you have defined a universal set of integers from one to ten.
Then you defined sets (presumably belong to the universal set) which combine ("unioned") to form a new set.
The first, {xx is multiple of 2} means the set of even numbers between 1 and 10, namely {2,4,6,8,10} and the second is
{xx is multiple of 7} which consists of only one element (between 1 and 10), namely {7}.
The union of these two sets give
{2,4,6,7,8,10}. 
MathMate,
I want to thank you so much in how you explained it. Thank you again and have a nice evening