Multiplication Review: Part 3
1. Multiplying with multiples of 10 (Tack on Trailing Zeros)
Here’s a trick for multiplying in your head.
5 x 30 = 5 x 3 tens = 15 x 10 = 150
7 x 400 = 7 x 4 hundreds = 28 x 100 = 2800
6 x 300 – 6 x 3 thousands = 18 x 1000 = 18 000
When one number has zeros at the end…
*Cut off (or hide) the end zeros.
*Multiply the remaining numbers.
* Tack the zeros you cut off (or hid) onto your answer.
9 x 5000 =
9 x 5 = 45 plus three zeros = 45 000
Practice:
1.
2.
3.
4.
5.
6.
7.
8.
8 x 80 =
10 x 7 =
9 x 30 =
80 x 4 =
12 x 20 =
5 x 500 =
900 x 2 =
3 x 300 =
9. 11 x 700 =
10. 4000 x 7 =
11. 7 x 3000 =
12. 6 x 600 =
13. 9 x 60 =
14. 7 x 800 =
15. 8 x 4000 =
2. Multiplying two multiples of 10.
50 x 300 =
To multiply the above numbers in your head…
*Cut off (or hide) the end zeros.
*Multiply the remaining numbers.
*Collect all the zeros and tack them onto your answer.
5 x 3 = 15.
Tack on the 0 from the 50, then the two 0s from the 300
50 x 300 = 15 000
Practice:
1. 80 x 80 =
2. 30 x 20 =
3. 40 x 70 =
4. 200 x 50 =
5. 30 x 300 =
6. 800 x 10 =
7. 800 x 70 =
8. 600 x 500 =
9. 700 x 300 =
10. 500 x 100 =
11. 40 x 800 =
12. 90 x 600 =
13. 50 x 40 =
14. 600 x 70 =
15. 900 x 90 =
3. Front-end Multiplying
Can you multiply this in your head?
52
X7
It’s easy if you break up one factor into smaller parts.
Break up 52…
50 + 2
52 = (50 + 2) x 7
= (50 x 7) + (2 x 7)
= 350 + 14
= 364
So 52 x 7 = 364 and
Practice:
1. 21 x 7 =
2. 41 x 2 =
3. 3 x 22 =
4. 6 x 74 =
5. 9 x 83 =
6. 55 x 5 =
7. 87 x 2 =
8. 4 x 45 =
7 x 52 = 364
and 52
X 7
364
9. 5 x 58 =
10. 2 x 76 =
11. 6 x 96 =
12. 2 x 48 =
13. 30 x 52 =
14. 20 x 25 =
15. 25 x 30 =