How do I multiply either column 1 or column 2 by same multiplier?

[broadoak8]

I have 4 columns of data ( #of units, old work price, new work price, &
total). How do I multiply number of units by either old work price, or new
work price, based on column where data is entered?

 

[John C]

assuming that the total is defined as #units X old work price (unless of
course there is a new work price, then it would be #units X new work price).
A2: #units, B2: old work price, C2: new work price
D2: =IF(C2="",B2,C2)*A2
If this isn't what you are looking for, give more info, based on what column
of what kind of data is entered?

 

[T. Valko]

Assuming that only one or the other will contain an entry:

=#of units * MAX(old work price, new work price)

=A1*MAX(B1,C1)