for example, i have this xml

<elements>
<a>
     <b>6</b> 
     <b>5</b>
     <b>6</b>
</a>
<a>
     <b>5</b>
     <b>5</b>
     <b>6</b>
</a>
<a>
     <b>5</b>
     <b>5</b>
     <b>5</b>
     <b>5</b>
</a>
</elements>

i need a xpath query, which must return me parent tag, only if all its children are equal to 5 (a[3] in this case). Something like that

//b[text()="5"]/..

but with check of all children's tags. Please note that number of children tags can be different from node to node.

It's possible with only xpath query?

thanks