Before you practice estimating products, look at the easy multiplication that can be done when the factors end in zeros.

You already know how to quickly multiply by 10, 100, 1000, etc…

You can find the products in questions like these using regular multiplication:

But here is a shortcut:

1. Count all the zeros at the end of the numbers in both factors.
2. Write down that many zeros at the end of the product.
3. Multiply the other digits in the usual way and put them before the zeros.

Exercise 1

Find the products using the shortcut. Check your work using the answer key at the end of the exercise.

1. [latex]\begin{array}{rr}&300\\\times&20\\\hline&6000\end{array}[/latex]
2. [latex]\begin{array}{rr}&6000\\\times&200\\\hline\\\end{array}[/latex]
3. [latex]\begin{array}{rr}&210\\\times&20\\\hline\\\end{array}[/latex]
4. [latex]\begin{array}{rr}&800\\\times&600\\\hline\\\end{array}[/latex]
5. [latex]\begin{array}{rr}&400\\\times&500\\\hline\\\end{array}[/latex]
6. [latex]\begin{array}{rr}&6000\\\times&90\\\hline\\\end{array}[/latex]
7. [latex]\begin{array}{rr}&50000\\\times&6000\\\hline\\\end{array}[/latex]
8. [latex]\begin{array}{rr}&80000\\\times&30\\\hline\\\end{array}[/latex]
9. [latex]\begin{array}{rr}&5000\\\times&50\\\hline\\\end{array}[/latex]
10. [latex]\begin{array}{rr}&70\\\times&80\\\hline\\\end{array}[/latex]
11. [latex]\begin{array}{rr}&3000\\\times&700\\\hline\\\end{array}[/latex]
12. [latex]\begin{array}{rr}&50000\\\times&900\\\hline\\\end{array}[/latex]
13. [latex]\begin{array}{rr}&9000\\\times&8000\\\hline\\\end{array}[/latex]
14. [latex]\begin{array}{rr}&60000\\\times&90\\\hline\\\end{array}[/latex]
15. [latex]\begin{array}{rr}&90000\\\times&2000\\\hline\\\end{array}[/latex]
16. [latex]\begin{array}{rr}&600\\\times&600\\\hline\\\end{array}[/latex]
17. [latex]\begin{array}{rr}&40000\\\times&800\\\hline\\\end{array}[/latex]
18. [latex]\begin{array}{rr}&2400\\\times&70\\\hline\\\end{array}[/latex]
19. [latex]\begin{array}{rr}&390\\\times&40\\\hline\\\end{array}[/latex]
20. [latex]\begin{array}{rr}&7200\\\times&5000\\\hline\\\end{array}[/latex]
21. [latex]\begin{array}{rr}&7000\\\times&7000\\\hline\\\end{array}[/latex]
22. [latex]\begin{array}{rr}&61000\\\times&400\\\hline\\\end{array}[/latex]
23. [latex]\begin{array}{rr}&5200\\\times&300\\\hline\\\end{array}[/latex]
24. [latex]\begin{array}{rr}&40\\\times&60\\\hline\\\end{array}[/latex]

Answers to Exercise 1

1. 6 000
2. 1 200 000
3. 4 200
4. 480 000
5. 200 000
6. 540 000
7. 300 000 000
8. 2 400 000
9. 250 000
10. 5 600
11. 2 100 000
12. 45 000 000
13. 72 000 000
14. 5 400 000
15. 180 000 000
16. 360 000
17. 32 000 000
18. 168 000
19. 15 600
20. 36 000 000
21. 49 000 000
22. 24 400 000
23. 1 560 000
24. 2 400

To find an estimated product, round the factors before you multiply. If a factor has only one digit, do not round it.

Topic C: Self-Test

Mark  /18    Aim  15/18

A. Multiply these numbers.

1. [latex]\begin{array}{rr}&600\\\times&70\\\hline\end{array}[/latex]
2. [latex]\begin{array}{rr}&9000\\\times&30\\\hline\end{array}[/latex]
3. [latex]\begin{array}{rr}&5000\\\times&600\\\hline\end{array}[/latex]
4. [latex]\begin{array}{rr}&3000\\\times&500\\\hline\end{array}[/latex]
5. [latex]\begin{array}{rr}&400\\\times&50\\\hline\end{array}[/latex]
6. [latex]\begin{array}{rr}&8000\\\times&1000\\\hline\end{array}[/latex]

B. Find an estimated product.

1. [latex]\begin{array}{rr}&87\\\times&23\\\hline\end{array}[/latex]
2. [latex]\begin{array}{rr}&268\\\times&25\\\hline\end{array}[/latex]
3. [latex]\begin{array}{rr}&9421\\\times&75\\\hline\end{array}[/latex]
4. [latex]\begin{array}{rr}&2632\\\times&49\\\hline\end{array}[/latex]
5. [latex]\begin{array}{rr}&365\\\times&455\\\hline\end{array}[/latex]
6. [latex]\begin{array}{rr}&7264\\\times&590\\\hline\end{array}[/latex]

Answers to Topic C Self Test

A. Multiply these numbers.

1. 42000
2. 270000
3. 3000000
4. 1500000
5. 20000
6. 8000000