1. 

let $countries := doc("http://mimuw.edu.pl/~henrykm/lab9/kraje/kraje.xml") 
for $item in $countries/countries/country
   where $item/@name = "Mongolia"
return data($item/@area)

Odpowiedz:
1565000

2. 

let $countries := doc("http://mimuw.edu.pl/~henrykm/lab9/kraje/kraje.xml") 
for $item in $countries/countries/country
   where some $item1 in $item/city satisfies 
       $item1/name = $item/@name
return (<name> {data($item/@name)} </name>) 

Odpowiedz:
<name>Mexico</name>
<name>Singapore</name>

3.

let $countries := doc("http://mimuw.edu.pl/~henrykm/lab9/kraje/kraje.xml") 
let $rus := 
( for $item in $countries/countries/country
   where $item/language= "Russian" 
   return $item)
return avg($rus/@population) 

Odpowiedz:
3.2017746666666668E7 

4.

let $countries := doc("http://mimuw.edu.pl/~henrykm/lab9/kraje/kraje.xml") 
let $ger := 
( for $item in $countries/countries/country
   where some $item1 in $item/language satisfies
       $item1 = "German" and $item1/@percentage > 50 
   return $item )
return data($ger/@name)

Odpowiedz:
Austria Germany Switzerland

5.

let $countries := doc("countries.xml") 
let $biggest := 
( for $item in $countries/countries/country
   where every $item1 in $countries/countries/country satisfies
       xs:int($item1/@population) <= xs:int($item/@population) 
   return $item )
return data($biggest/@name)

Odpowiedz:
China