The speed mathematics method (Bài đọc Phương pháp tính toán nhanh, đính kèm file)
Bạn đọc và gạch dưới hoặc khoanh tròn những từ đã học (có thể mở rộng những từ chưa được học). Nếu có thời gian, thực hiện các phép tính trong bài.
Tính kết quả 8×6.
Bước 1: Khoanh tròn dưới số 8 và 6, sau đó điền vào một số mà cộng với số trên sẽ được 10. Vậy dưới số 8 là 2, dưới số 6 là 4.
Bước 2: Thực hiện lấy kết quả của trừ chéo (8-4, 6-2), đều được 4. Viết 4 phía sau dấu bằng.
Bước 3: Lấy hai số dưới nhân lại với nhau (2×4), được 8. Ghi số 8 tiếp theo số 4 (đã thực hiện tại Bước 2), được kết quả của phép tính (48).
Post in the same topic: Calculations vocabulary for math
THE SPEED MATHEMATICS METHOD
I am now going to show you the speed mathematics way of working this out. The first step is to draw circles under each of the numbers.
The problem now looks like this:
We now look at each number and ask, how many more do we need to make 10?
We start with the 8. If we have 8, how many more do we need to make 10?
The answer is 2. Eight plus 2 equals 10. We write 2 in the circle below the 8. Our equation now looks like this:
We now go to the 6. How many more to make 10? The answer is 4.
We write 4 in the circle below the 6.
This is how the problem looks now:
We now take away, or subtract, crossways or diagonally. We either take 2 from 6 or 4 from 8. It doesn’t matter which way we subtract—
the answer will be the same, so choose the calculation that looks easier. Two from 6 is 4, or 4 from 8 is 4. Either way the answer is 4.
You only take away one time. Write 4 after the equals sign.
For the last part of the answer, you “times,” or multiply, the numbers in the circles. What is 2 times 4? Two times 4 means two fours added together. Two fours are 8. Write the 8 as the last part of the answer.
The answer is 48.
Easy, wasn’t it? This is much easier than repeating your multiplication tables every day until you remember them. And this way, it doesn’t matter if you forget the answer, because you can simply work it out again.
Do you want to try another one? Let’s try 7 times 8. We write the problem and draw circles below the numbers as before:
How many more do we need to make 10? With the first number, 7, we need 3, so we write 3 in the circle below the 7. Now go to the 8.
How many more to make 10? The answer is 2, so we write 2 in the circle below the 8.
Our problem now looks like this:
Now take away crossways. Either take 3 from 8 or 2 from 7.
Whichever way we do it, we get the same answer. Seven minus 2 is 5 or 8 minus 3 is 5. Five is our answer either way. Five is the first digit of the answer. You only do this calculation once, so choose the way that looks easier.
The calculation now looks like this:
For the final digit of the answer we multiply the numbers in the circles: 3 times 2 (or 2 times 3) is 6. Write the 6 as the second digit of the answer.
Here is the finished calculation:
Seven eights are 56.
How would you solve this problem in your head? Take both numbers from 10 to get 3 and 2 in the circles. Take away crossways. Seven minus 2 is 5. We don’t say five, we say, “Fifty . . .” Then multiply the numbers in the circles. Three times 2 is 6. We would say, “Fifty . . . six.”
With a little practice you will be able to give an instant answer. And, after calculating 7 times 8 a dozen or so times, you will find you remember the answer, so you are learning your tables as you go.
Here are some problems to try by yourself. Do all of the problems, even if you know your tables well. This is the basic strategy we will use for almost all of our multiplication.
a) 9 × 9 = e) 8 × 9 =
b) 8 × 8 = f) 9 × 6 =
c) 7 × 7 = g) 5 × 9 =
d) 7 × 9 = h) 8 × 7 =
a) 81 e) 72
b) 64 f) 54
c) 49 g) 45
d) 63 h) 56