To sum every nth column, you can use a formula based on the SUMPRODUCT, MOD, and COLUMN functions.
In the example shown, the formula in L5 is:
=SUMPRODUCT(--(MOD(COLUMN(B5:J5)-COLUMN(B5)+1,K5)=0),B5:J5)
How this...

Excel handles dates and time using a scheme in which dates are serial numbers and times are fractional values. For example, June 1, 2000 12:00 PM is represented in Excel as the number 36678.5, where 36678 is the date...

To convert a measurement in inches to inches and feet (i.e. 53 to 4' 5") you can use a formula based on the INT and MOD functions. In the example shown, the formula in D5 is:
=INT(B5/12)&"' "&MOD(B5,...

To allow only numbers in multiples of 100, you can use data validation with a custom formula based on the MOD function. In the example shown, the data validation applied to C5:C10 is:
=MOD(C5,100)=0
How this formula...

To get the duration between two times in as decimal hour (i.e. 3 hrs, 4.5 hrs, 8 hrs, etc.) you can use a formula based on the MOD function.
In the example shown, the formula in D5 is:
=MOD(B2-A2,1)*24
Excel hours...

To generate a fixed value every N columns (for example, a fixed expense every 3 months, a fixed payment every 6 months, etc.) you can use a formula based on the MOD function.
In the example shown, generate a value of...

To calculate the number of hours between two times, you can use a formula that simply subtracts the start time from the end time. This is useful to calculate working time, calculate elapsed time, etc. However, when...

To add an ordinal suffix to a number (i.e. 1st, 2nd, 3rd, etc.) you can use a formula based on the CHOOSE function to assign the suffix.
In the example shown, the formula in C5 is:
=CHOOSE(B5,"st","nd...

If you want to find the most recent Wednesday, or Saturday, or Monday, given a specific start date, you can use a formula that uses the MOD function.
How the formula works
Formulas that use the concept of "day of week...

To add a given number of hours to a time, you can add hours divided by 24, or use the TIME function.
In the example shown, the formula in D5 is:
=B5+(C5/24)
Note: make sure results are formatted as time.
How this...

To convert a time from one time zone to another, you can use a formula that converts hours entered as whole numbers to the decimal values that Excel recognizes as times. In the example shown, the formula in F5 is:
=...

To calculate work hours, taking into account break time that needs to be subtracted, you can use a formula based on the MOD function. MOD is used to handle start and end times that cross midnight. In the example shown,...

To highlight numbers that are multiples of a another number with conditional formatting, you can use a simple formula based on the MOD function.
In the example shown, the formula used to highlight multiples of 9 is...

To get the number at a specific place value you can use a formula based on the MOD function. By place value, we mean hundred thousands, ten thousands, thousands, hundreds, tens, ones, etc.
In the example shown, the...

To add a given number of minutes to a time, you can add minutes divided by 1440, or use the TIME function.
In the example shown, the formula in D5 is:
=B5+(C5/1440)
Note: make sure results are formatted as time....