Matemática Elementar

Problema 1

Add these two-digit numbers. Show your work.

a) $23 + 45 = \underline{\quad}$

b) $34 + 52 = \underline{\quad}$

c) $17 + 61 = \underline{\quad}$

d) Now add all three answers together: $\underline{\quad} + \underline{\quad} + \underline{\quad} = \underline{\quad}$

Problemas

1. Add these two-digit numbers. Show your work.

a) $23 + 45 = \underline{\quad}$

b) $34 + 52 = \underline{\quad}$

c) $17 + 61 = \underline{\quad}$

d) Now add all three answers together: $\underline{\quad} + \underline{\quad} + \underline{\quad} = \underline{\quad}$

2. A toy store sold $26$ dolls, $38$ puzzles, $14$ board games, and $12$ stuffed animals in one week.

Add all four numbers to find the total toys sold:

$26 + 38 + 14 + 12 = \underline{\quad}$

(Hint: look for pairs that are easy to add first!)

3. Use mental math. Add or subtract $10$ or $100$ .

a) $47 + 10 = \underline{\quad}$

b) $83 - 10 = \underline{\quad}$

c) $250 + 100 = \underline{\quad}$

d) $460 - 100 = \underline{\quad}$

e) $99 + 10 = \underline{\quad}$

f) $300 - 100 = \underline{\quad}$

4. Explain how you solved each problem. Use words like "tens," "ones," and "hundreds."

a) $36 + 27 = \underline{\quad}$

Explain your strategy: $\underline{\quad\quad\quad\quad\quad\quad}$

b) $54 - 18 = \underline{\quad}$

Explain your strategy: $\underline{\quad\quad\quad\quad\quad\quad}$

5. A school is collecting cans for a food drive. Here is what each class collected:

| Class | Cans | |---|---| | Room A | $45$ | | Room B | $32$ | | Room C | $18$ | | Room D | $25$ |

a) How many cans did Room A and Room B collect together? $45 + 32 = \underline{\quad}$

b) How many cans did all four rooms collect in total? $\underline{\quad}$

c) The school goal was $150$ cans. Did they reach the goal? By how much did they go over or fall short?

Gabarito — Addition to 1000

1. a) $23 + 45 = 68$ . Add tens: $20 + 40 = 60$ . Add ones: $3 + 5 = 8$ . Total: $68$ .

b) $34 + 52 = 86$ . Add tens: $30 + 50 = 80$ . Add ones: $4 + 2 = 6$ . Total: $86$ .

c) $17 + 61 = 78$ . Add tens: $10 + 60 = 70$ . Add ones: $7 + 1 = 8$ . Total: $78$ .

d) $68 + 86 + 78 = 232$ . One way: $68 + 86 = 154$ , then $154 + 78 = 232$ .

2. Look for pairs that make addition easier:

$26 + 14 = 40$ (the ones make $10$ !)

$38 + 12 = 50$ (the ones also make $10$ !)

Now add the two results: $40 + 50 = 90$ .

Total toys sold: $90$ .

3. a) $47 + 10 = 57$ . Adding $10$ increases the tens digit by $1$ .

b) $83 - 10 = 73$ . Subtracting $10$ decreases the tens digit by $1$ .

c) $250 + 100 = 350$ . Adding $100$ increases the hundreds digit by $1$ .

d) $460 - 100 = 360$ . Subtracting $100$ decreases the hundreds digit by $1$ .

e) $99 + 10 = 109$ . The tens and ones "roll over" — $9$ tens $+ 1$ ten $= 10$ tens $= 1$ hundred.

f) $300 - 100 = 200$ .

4. a) $36 + 27 = 63$

Example strategy: "I added the tens first: $30 + 20 = 50$ . Then I added the ones: $6 + 7 = 13$ . Since $13$ has $1$ extra ten, I added it to $50$ : $50 + 13 = 63$ ."

Another valid strategy: "I broke $27$ into $24 + 3$ . Then $36 + 24 = 60$ (easy!), and $60 + 3 = 63$ ."

b) $54 - 18 = 36$

Example strategy: "I subtracted $20$ from $54$ to get $34$ (going $2$ too far). Then I added $2$ back: $34 + 2 = 36$ ."

Another valid strategy: "I counted up from $18$ : $18 + 2 = 20$ , $20 + 34 = 54$ , so $2 + 34 = 36$ ."

5. a) $45 + 32 = 77$ cans.

b) $45 + 32 + 18 + 25$ . One way: $45 + 25 = 70$ and $32 + 18 = 50$ . Then $70 + 50 = 120$ cans total.

c) The goal was $150$ cans. They collected $120$ cans. $150 - 120 = 30$ . They fell short by $30$ cans.