Table:
0
A
B
C
D
E
1
account id
customer id
date account opened
account name
other account details
2
1
8
7/30/2016 22:22
900
Regular
3
2
3
5/29/2017 16:45
520
VIP
4
3
8
5/4/2012 18:50
323
Regular
5
4
15
3/29/2011 15:06
390
VIP
6
5
15
8/11/2014 18:15
935
Regular
7
6
12
5/30/2014 12:16
371
Regular
8
7
13
11/3/2015 8:04
398
VIP
9
8
9
6/13/2009 11:41
710
Regular
10
9
8
10/22/2010 13:33
337
Regular
11
10
15
4/25/2016 21:49
429
VIP
12
11
13
7/9/2012 23:40
191
VIP
13
12
8
2/2/2015 9:47
601
Regular
14
13
13
6/16/2010 9:35
272
Regular
15
14
13
12/28/2014 7:29
861
VIP
16
15
6
5/4/2008 22:15
662
VIP

Questions and formulas:
Question: Show the number of accounts.
Formula: SUM(A1)
Formula2: SUM(A2:A16)
Level: easy
Question: How many accounts are there?
Formula: SUM(A1)
Formula2: SUM(A2:A16)
Level: easy
Question: How many customers have opened an account?
Formula: ROWS(UNIQUE(B1))
Formula2: ROWS(UNIQUE(B2:B16))
Level: easy
Question: Count the number of customers who have an account.
Formula: ROWS(UNIQUE(B1))
Formula2: ROWS(UNIQUE(B2:B16))
Level: easy
Question: Show the id, the date of account opened, the account name, and other account detail for all accounts.
Formula: CHOOSE({1,2,3,4},A1,C1,D1,E1)
Formula2: CHOOSE({1,2,3,4},A2:A16,C2:C16,D2:D16,E2:E16)
Level: easy
Question: What are the ids, date opened, name, and other details for all accounts?
Formula: CHOOSE({1,2,3,4},A1,C1,D1,E1)
Formula2: CHOOSE({1,2,3,4},A2:A16,C2:C16,D2:D16,E2:E16)
Level: easy
Question: How many accounts does each customer have? List the number and customer id.
Formula: SUMMARIZE(B1,SUMX(A1))
Formula2: SUMMARIZE(B2:B16,SUMX(A2:A16))
Level: easy
Question: Count the number of accounts corresponding to each customer id.
Formula: SUMMARIZE(B1,SUMX(A1))
Formula2: SUMMARIZE(B2:B16,SUMX(A2:A16))
Level: easy
Question: Number of customers opening an account for each date?
Formula: SUMMARIZE(C1,SUMX(B1))
Formula2: SUMMARIZE(C2:C16,SUMX(B2:B16))
Level: easy
Question: Total customers and total accounts opened respectively
Formula: HSTACK(SUM(B1), ROWS(UNIQUE(C1)))
Formula2: HSTACK(SUM(B2:B16), ROWS(UNIQUE(C2:C16)))
Level: hard
Question: How many accounts does each customer open?
Formula: SUMMARIZE(B1,SUMX(A1))
Formula2: SUMMARIZE(B2:B16,SUMX(A2:A16))
Level: easy
Question: How many customers have opened an account on each date? 
Formula: SUMMARIZE(C1,SUMX(B1))
Formula2: SUMMARIZE(C2:C16,SUMX(B2:B16))
Level: easy
Question: The number of customers and number of accounts opened.
Formula: HSTACK(SUM(B1), ROWS(UNIQUE(C1)))
Formula2: HSTACK(SUM(B2:B16), ROWS(UNIQUE(C2:C16)))
Level: hard