# Adding numbers of different things

##### Full Member
I mean while I add numbers, it's not actually must be all the numbers of the same units, I can ask for example: how many chairs and tables we have? then the answer is 3[charis]+3[tables] = 6 so however they're not the same units we added them as same units .. like something magic..

#### Dr.Peterson

##### Elite Member
It IS necessary to add things of the same type; you can't just say the answer is 6. If you add abstract numbers like 3+3, you get 6; but if they are "denominate numbers" with units, you can't add them until they have the same unit. Doing so is not magic; it's an error.

To answer a similar, common question, if you want to add 3 apples + 3 oranges, you have to call it 6 pieces of fruit (or else 6 cups of fruit salad).

This is very similar to the need to use a common denominator to add fractions: you can't add 1 half + 1 third; you have to convert them to something like 3 sixths + 2 sixths = 5 sixths.

#### pka

##### Elite Member
I already discussed about units but there's something still weird for me which is:
lets assume I have 3 chairs and 3 tables, so I have 3[chairs] , 3[tables] , so lets assume I have an equation that says to assign the number of chairs and number of tables you have to add them, so in my case I must do 3+3=6 but how can I add two amounts of different units as same units?!!! doesn't it weird?!
Suppose there is a testing room with six tables and two chairs at each table. There is nothing more in the room.
How would you answer each of these?
How many pieces of furniture are there in the room?
How many tables and chairs are there on that room?
How many tables or chairs are there on that room?
Are these all the same question?

##### Full Member
Suppose there is a testing room with six tables and two chairs at each table. There is nothing more in the room.
How would you answer each of these?
How many pieces of furniture are there in the room?
How many tables and chairs are there on that room?
How many tables or chairs are there on that room?
Are these all the same question?
I was thinking that if it's given 3 [chairs] then the unit must be assigned with the number itself, but it's totally different, it's related to the question itself, so might the unit be added or might the number itself of the "unit" be added! so it's totally different between "unit" and between "number"

#### Jomo

##### Elite Member
Have you been to the supermarket where the express lane says 10 items or less? You do NOT have to buy the same 10 or less items to use this express lane. In fact you can buy all different items.

Many years ago my friend said he could just look at the grocery cart and say how much the total would be. I said I could do better than him. As the cashier rung up the prices I just added the dollar amount and the number of items. My method was to take the total of the dollar amount and add on half of the number of items (another words I assumed that each item had the cents equal to \$.50) and I came closer than my friend to the actual total. More importantly I added the number of items purchased even though they were different items