Question

find the product. check whether your answer is reasonable.

1. estimate: 600

629 × 5 = 1350

1. estimate: _____

7 × 186 = 3150

1. estimate: _____

453 × 3 = _____
compare.

1. 3 × 627 ○ 5 × 379
2. 192 × 9 ○ 293 × 4
3. a square city block has a side length of 394 feet. you walk around the block once. how many feet do you walk?

_____ feet

1. dig deeper without multiplying, explain how you can determine which product is greater.

3 × 278 ○ 2 × 391

1. you be the teacher your friend says that the product of a three - digit number and a one - digit number is always a three - digit number. is your friend correct? explain.
2. model real life the numbers of songs newton and descartes download are shown. you download 2 times as many songs as descartes. who downloads the most songs?

newton: 351 songs
descartes: 167 songs
review & refresh
find the sum or difference. use the inverse operation to check.
16.
\begin{array}{r}847\\ - 162\\ hlineend{array}
17.
\begin{array}{r}612\\ + 289\\ hlineend{array}
18.
\begin{array}{r}500\\ - 351\\ hlineend{array}

Explanation:

Problem 7

Step1: Estimate \(629\times5\)

Round \(629\) to \(600\), then \(600\times5 = 3000\).

Step2: Calculate \(629\times5\)

\(629\times5=(600 + 29)\times5=600\times5+29\times5 = 3000+145 = 3145\).

Step1: Estimate \(7\times186\)

Round \(186\) to \(200\), then \(7\times200 = 1400\).

Step2: Calculate \(7\times186\)

\(7\times186 = 7\times(180 + 6)=7\times180+7\times6=1260 + 42 = 1302\).

Step1: Estimate \(453\times3\)

Round \(453\) to \(450\), then \(450\times3 = 1350\).

Step2: Calculate \(453\times3\)

\(453\times3=(450 + 3)\times3=450\times3+3\times3 = 1350+9 = 1359\).

Answer:

Estimate: \(3000\), Product: \(3145\)

Problem 8