Main content

### Course: 5th grade > Unit 2

Lesson 4: Adding decimals (hundredths)# Add decimals: FAQ

Frequently asked questions about adding decimals.

## How do we estimate with adding decimals?

Estimating with adding decimals means finding an approximate answer by rounding the decimals to the nearest whole number, tenth, or hundredth.

For example, if we want to estimate the sum of $12.34$ and $5.67$ , we can round both numbers to the nearest tenth: $12.34\approx 12.3$ and $5.67\approx 5.7$ . Then, we can add the rounded numbers: $12.3+5.7=18$ . Estimating can help us check if our answer is reasonable or if we made a mistake.

Try it yourself with this exercise:

## How do we add decimals visually?

We can add decimals visually using grids. A grid is a square that is divided into smaller squares. We can use the grid to show how much of a whole unit we have.

For example, if we want to add $0.4$ and $0.3$ , we can use a grid that has $10$ squares in each row and column. Each square represents one-tenth or $0.1$ . To show $0.4$ , we can shade $4$ squares in one row. To show $0.3$ , we can shade $3$ squares in another row. To find the sum, we can count how many squares are shaded in total. We have $7$ shaded squares, which means the sum is $0.7$ .

Try it yourself with this exercise:

## How do we add decimals and whole numbers that have different number of decimal places?

To add decimals and whole numbers that have different number of decimal places, we can use zeros as placeholders to make them have the same number of decimal places. Then, we can use a place value chart to add each place value column.

Ones | Tenths | ||
---|---|---|---|

Try it yourself with this exercise:

## Where do we use adding decimals in the real world?

We use adding decimals in the real world whenever we deal with money, measurements, or fractions of things. For example, if we want to buy a book that costs $7.99$ and a pencil that costs $0.25$ , we need to add the decimals to find the total cost. We get $7.99+0.25=8.24$ . Another example is if we want to measure the length of a table that is $1.2$ meters long and a chair that is $0.65$ meters long. We need to add the decimals to find the total length. We get $1.2+0.65=1.85$ .

## Want to join the conversation?

- im having a hard time understanding these can someone help me(15 votes)
- Here is a summary as best as I can put it:

In the first section, they are talking about adding two numbers using rounding. If you have two numbers like 12.34 and 34.78 and you want to make it a bit easier you could round the two numbers. 12.34 would become 12.3 and 34.78 rounded would become 34.8. Then you would add those two numbers. The answer would be around 47.1. Basically the section is just explaining another way to add decimals while using rounding.

The second section is talking about adding decimals with grids. A grid is a square made up of other smaller squares. It is a bit like a multiplication table. Khan Academy uses grids a lot. If you want to have numbers going up to ten then you might have a 10 by 10 grid with 10 square going up and 10 squares going to the right. You can do the same thing for decimals. To get to 1 you might have 10 squares going up and 10 going to the right. Each square would be a decimals from 0.1 to 1.0. You can shade in the amount of squares you need to get the answer to whatever you are doing.

The third section is explaining how you would add two numbers with a different amount of decimals. Like 2.93 and 3.4. You have 3 hundreths in the first number but no hundreths in the second number. You would just simply put a zero in the hundreth's place and make the number 3.40. Then you could add the two numbers.

The last section is just explaining different situations where you would use decimals in the real world. Like when you buy or sell things.

Did I explain it ok? Is there anything I missed? I hope this helps some. :)(44 votes)

- how would you add 0.99 and 0.23(3 votes)
- 0.99

0.23

------

1.22

remember to carry the 1 !(5 votes)

- whats is 1.2 + 9.86(3 votes)
`1.2 + 9.86 = 11.06`

It may help you to view it as`9.86 + 1.2`

instead!(3 votes)

- how do you add decimals and whole numbers(2 votes)
- if you want to do something like that, try this for example: 1.45

2.53

----+ hope this helps :)

3.98(3 votes)

- I just want to say everybody is amazing and smart! You can solve anything! :)(1 vote)
- Who is the guy making the videos?(0 votes)
- how do you know where the decimal goes?(0 votes)
- it goes right to the ones place(2 votes)