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Using LunchMath™

There are only two required fields to use the LunchMath program: Total, and Num. People. Enter a total, the number of people splitting the bill, and then move the slider back and forth to see the Tip, Per Person cost, and the amount you have to pay (Pay This) change. The values are rounded up to the nearest 25 cent value. If you enter a Subtotal, LunchMath will calculate the tip based on the subtotal.

Figure 1 shows an example of four people splitting a bill for $107. The tip is set to about 15%. Since no subtotal was entered, the tip will be based on the Total, $107.

You can adjust the meal cost of up to 4 people. You have the option of adjusting the costs by putting one of the following values in the Adjust field:

  • Enter the absolute value of a person's meal excluding tax and tip.
  • Enter "+" and a number (e.g., +3.50) if a person's meal was more than the average meal cost.
  • Enter "-" and a number (e.g., -5) if a person's meal was less than the average meal cost.

If you put a value in the Paid field, the amount of change the person is owed will be displayed in the Chng field. The change value is based on the Pay field if a value is present — otherwise it will be based on the Per Person value. Note: the words Per Person change to Rest Owe if any adjusted values are entered.

If everyone has similarly priced meals but one person has water while everyone else had a $2.75 drink, then enter -2.75 in the Adjust field. LunchMath will take out the $2.75 from that meal and calculate the tip (and tax if the subtotal was entered). Again, the numbers are all rounded up to the nearest 25 cents. You can also enter a positive number, e.g., +2.75 if one person's meal costs more.

Figure 2 shows an example in which the first two people ordered the same priced meal. The third person (BJ) ordered a meal that cost $5 less than that of the first two people before tax and tip. The fourth person's (VD's) meal cost $20 before tax and tip. The subtotal was entered and the tip was set to about 18% to give round numbers. The first two people owe $16.25 each as reflected in the renamed field: Rest Owe. The tax and tip are calculated for BJ's meal, giving him a total of $10. The tax and tip are added to VD's meal, giving him a total of $25. Additionally, we can see in the Paid field that one of the first two people put in $20 to cover their portion of the bill ($16.25). The Chng column shows that this person gets back $3.75 in change.

Figure 3 shows the same example as Figure 2 with the tip set to 0% and Round turned Off. Turning the Round option off tells the program not to make any adjustments to the calculations. You can see that the re is a value in the Tip field even though the tip percentage is set to 0%. This indicates that the Total amount could not be evenly divided with the parameters entered. The Tip field shows that there is 14 cents extra after everyone puts in their contribution.

If the tip is set to 0% but the amounts are not evenly divisible by Num. People, the program will calculate final rounded amounts but there may be some small amount left over in the Tip field.

LunchMath also handles cases where a discount is applied to the bill. In the following cases, the bill contains the subtotoal, the discount amount, then the adjusted total.

Case 1: If the bill is to be split evenly and the discount is to be applied to everyone in the party simply enter the Subtotal, Total, and Num. People fields as they are shown on the bill. LunchMath will calculate the Tip based on the Subtotal. The Per Person amount will include the correct tip even though the Total amount may be less than the Subtotal amount. The Rest Owe field will show the amounts the rest of the party owe.

Case 2: If the bill is split evenly and the discount is to only be applied to one person, enter the Subtotal, Total, and Num. People as above. Now however, enter the discount amount in one of the Adjust fields. If the discount was for $10 off, enter -10 in an Adjust field. LunchMath will calculate the Pay amount for the person getting the discount, including their portion of the tax and tip.

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