Matemática Elementar

Problema 1

Add a two-digit number and a one-digit number.

$34 + 5 = \underline{\quad}$

Think: $34$ has $3$ tens and $4$ ones. Add $5$ ones: $4 + 5 = \underline{\quad}$ ones.

So $34 + 5 = 3$ tens and $\underline{\quad}$ ones $= \underline{\quad}$

Problemas

1. Add a two-digit number and a one-digit number.

$34 + 5 = \underline{\quad}$

Think: $34$ has $3$ tens and $4$ ones. Add $5$ ones: $4 + 5 = \underline{\quad}$ ones.

So $34 + 5 = 3$ tens and $\underline{\quad}$ ones $= \underline{\quad}$

2. Add the ones first, then write the answer.

$52 + 7 = \underline{\quad}$

$61 + 8 = \underline{\quad}$

$43 + 6 = \underline{\quad}$

3. Add multiples of 10.

$20 + 30 = \underline{\quad}$

$40 + 50 = \underline{\quad}$

$10 + 70 = \underline{\quad}$

Think: $2$ tens $+ 3$ tens $= \underline{\quad}$ tens $= \underline{\quad}$

4. A classroom has $24$ crayons in one box and $5$ more crayons on a table.

How many crayons are there in all?

$24 + 5 = \underline{\quad}$

Another classroom has $30$ crayons and gets $20$ more.

$30 + 20 = \underline{\quad}$

5. Fill in the missing number.

$46 + \underline{\quad} = 49$

$\underline{\quad} + 20 = 70$

$55 + \underline{\quad} = 58$

Gabarito — Adding Two-Digit Numbers

1. $34 = 3$ tens and $4$ ones.

Add $5$ ones to the ones place: $4 + 5 = 9$ ones.

$34 + 5 = 3 \text{ tens and } 9 \text{ ones} = \mathbf{39}$

2. Add the ones; the tens stay the same:

$52 + 7 = 59 \quad (2 + 7 = 9 \text{ ones})$ $61 + 8 = 69 \quad (1 + 8 = 9 \text{ ones})$ $43 + 6 = 49 \quad (3 + 6 = 9 \text{ ones})$

3. When adding multiples of $10$ , only the tens digit changes:

$20 + 30 = 50 \quad (2 \text{ tens} + 3 \text{ tens} = 5 \text{ tens})$ $40 + 50 = 90 \quad (4 \text{ tens} + 5 \text{ tens} = 9 \text{ tens})$ $10 + 70 = 80 \quad (1 \text{ ten} + 7 \text{ tens} = 8 \text{ tens})$

4. $24 + 5 = 29 \text{ crayons total}$

$30 + 20 = 50 \text{ crayons total}$

5. Find the missing number by thinking about what is needed:

$46 + \mathbf{3} = 49 \quad (49 - 46 = 3)$ $\mathbf{50} + 20 = 70 \quad (70 - 20 = 50)$ $55 + \mathbf{3} = 58 \quad (58 - 55 = 3)$