How do I formulate (d-c) +(b-a) or d-a in the same cell?

Question

I'm trying to create a formula in Numbers. I have 4 columns to enter time data (for daycare). On some days, kids have school. I need a formula that will total the hours depending on school (d-c) + (b-a) or for when I have them the full day (d-a). I need it to be able to use first formula if all 4 columns have entries and if not to use second formula.

Answer 1

Hello
Actually you only need one formula: D-A-(C-B).
A pitfall in Numbers is date-time value. There's no time-only value and if you input 12:00 in a cell, the date is automatically assumed to be today's date. Because of this, you'd have to be very careful in handling values which look like time-only value but actually date-time value. (If you input A, B, C and D on different days, simple D-A-(C-B) won't yield the expected result.)
One way around this annoying issue is to use HHMM or HHMMSS notation for time-only value which is indeed nothing but a number and calculate the quasi time-only value by TIME(HH,MM,SS) function. TIME() function returns a date-time value of which date is the constant epoch date, that is 1904-01-01.
E.g.,
Table 1
A1  a
A2  1200
A3  1300
A4 
B1  b
B2  1400
B3 
B4 
C1  c
C2  1430
C3 
C4 
D1  d
D2  1700
D3  1600
D4 
E1  d-a-(c-b)
E2  =I2-F2-(H2-G2)
E3  =I3-F3-(H3-G3)
E4  =I4-F4-(H4-G4)
F1 
F2  =TIME(INT(A2/100),MOD(A2,100),0)
F3  =TIME(INT(A3/100),MOD(A3,100),0)
F4  =TIME(INT(A4/100),MOD(A4,100),0)
G1 
G2  =TIME(INT(B2/100),MOD(B2,100),0)
G3  =TIME(INT(B3/100),MOD(B3,100),0)
G4  =TIME(INT(B4/100),MOD(B4,100),0)
H1 
H2  =TIME(INT(C2/100),MOD(C2,100),0)
H3  =TIME(INT(C3/100),MOD(C3,100),0)
H4  =TIME(INT(C4/100),MOD(C4,100),0)
I1 
I2  =TIME(INT(D2/100),MOD(D2,100),0)
I3  =TIME(INT(D3/100),MOD(D3,100),0)
I4  =TIME(INT(D4/100),MOD(D4,100),0)
* You may fill down and fill right the formula in F2 and fill down the formula in E2.
Table is built in Numbers v2.
Good luck,
H