Table:
0
A
B
C
D
1
employee id
name
age
city
2
1
George Chuter
23
Bristol
3
2
Lee Mears
29
Bath
4
3
Mark Regan
43
Bristol
5
4
Jason Hobson
30
Bristol
6
5
Tim Payne
29
Wasps
7
6
Andrew Sheridan
28
Sale
8
7
Matt Stevens
29
Bath
9
8
Phil Vickery
40
Wasps
10
9
Steve Borthwick
32
Bath
11
10
Louis Deacon
36
Leicester

Questions and formulas:
Question: How many employees are there within each city?
Formula: SUMMARIZE(D1,SUMX(A1))
Formula2: SUMMARIZE(D2:D11,SUMX(A2:A11))
Level: easy
Question: How many employees work in each city?
Formula: SUMMARIZE(D1,SUMX(A1))
Formula2: SUMMARIZE(D2:D11,SUMX(A2:A11))
Level: easy
Question: Cities which have more than one employee aged 30.
Formula: LET(query1,SUMMARIZE(D1,SUMX(A1),SUMX(C1)),FILTER(query1,(CHOOSECOLS(query1,3)=30)*(CHOOSECOLS(query1,4)>1)))
Formula2: LET(query1,SUMMARIZE(D2:D11,SUMX(A2:A11),SUMX(C2:C11)),FILTER(query1,(CHOOSECOLS(query1,3)=30)*(CHOOSECOLS(query1,4)>1)))
Level: hard
Question: How many employees in each city?
Formula: SUMMARIZE(D1,SUMX(A1))
Formula2: SUMMARIZE(D2:D11,SUMX(A2:A11))
Level: easy
Question: the city having more than 1 employees aged 30
Formula: LET(query1,SUMMARIZE(D1,SUMX(A1),SUMX(C1)),FILTER(query1,(CHOOSECOLS(query1,3)=30)*(CHOOSECOLS(query1,4)>1)))
Formula2: LET(query1,SUMMARIZE(D2:D11,SUMX(A2:A11),SUMX(C2:C11)),FILTER(query1,(CHOOSECOLS(query1,3)=30)*(CHOOSECOLS(query1,4)>1)))
Level: hard