Since we were little, we have been playing adding numbers, whether adding the fingers and toes, or adding the age of our colleagues. However, it is necessary to understand how this addition is done “mathematically”. You will see that it is not difficult at all.
Do you still remember how we organize the numbers? Through the houses: one, ten, hundred, thousand. Remembered? Well, this will be of great importance for us to organize our addition.
Let's look at the following little problem:
“A group of friends from a classroom got together to buy a video game, however the friends are in doubt whether all of their money will be enough to buy this video game. We know that the toy costs 400 reais and that each member of this group has the following amount: Lucas – 39 reais; Joaquim – 201 reais; Pedro – 55 reais; Luciana – 105 reais”.
To know how many reais these students have together, we must add up the money from all of them, correct?
Let's do this sum, putting a hundred under a hundred, a ten under a ten, and a unit under a unit.
| Hundred | ten | Unit | |
| Lucas | 3 | 9 | |
| Joaquim | 2 | 0 | 1 |
| Peter | 5 | 5 | |
| Luciana | 1 | 0 | 5 |
Adding the units together, we will have:
39
201 +
55
105
20 units (turning into 0 units and 2 tens, we raise the 2 to the tens)
2
39
201 +
55
105
0
Adding the tens we will have 10 tens, which is equivalent to 1 hundred and 0 tens, so we go up 1 hundred to the hundreds place.
1
39
201 +
55
105
00
Adding up the hundreds we will have 4 hundreds.
Therefore, the sum of the friends' money is given by:
39
201 +
55
105
400 reais.
That is, they have enough money to buy the video game.
By Gabriel Alessandro de Oliveira
Graduated in Mathematics
