"Approximate Numbers" PPT Courseware 3

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"Approximate Numbers" PPT Courseware 3

August 1, 2006, 3 days, approximately 4.3 million yuan

Do you think there is any difference between these numbers in life?

In life, we need not only accurate numbers but also approximate numbers!!

What methods have we learned to approximate numbers?

"Rounding" is a commonly used method for us to approximate a number. Usually, when we use the "rounding method" to approximate a number, the digit that we round to is the precise digit of the approximate number.

Use the "rounding" method to approximate the value of π as required

Accurate to single digit (accurate to 1) π≈3

Accurate to tenths (accurate to 0.1)π≈3.1

Accurate to percentile (accurate to 0.01)π≈3.14

Accurate to thousandths (accurate to 0.001)π≈3.142

The following are approximate numbers obtained by rounding. Please indicate their significant digits:

3.010 has 4 significant digits 3, 0, 1, 0;

0.206 has three significant digits: 2, 0, and 6;

400 has three valid digits 4, 0, and 0.

Note 1) When judging valid digits, pay attention to the numbers at the starting and ending positions and "0".

2) "Accurate to which digit" depends on the digit of the last digit.

Small scale chopper:

1. Among the following data (the underlined part), which one is not an approximate number ( )

(A) At the 2004 Athens Olympics, Liu Xiang’s 110m hurdles time was 12.91 s;

(B) The world’s population has reached 6.5 billion;

(C) Indian Ocean tsunami, the international community donated more than 4 billion US dollars in donations and materials to the disaster area;

(D) The People's Republic of China has 32 provincial-level administrative units.

2. The following approximate numbers are obtained by rounding, fill in the blanks:

(1) 0.030 is accurate to ( ) digits, there are ( ) significant digits, and the significant digits are ( ).

(2) 2000 is accurate to ( ), there are ( ) significant figures, and the significant figures are ( )

3. Use rounding to get an approximate number:

(1) 4.048 (accurate to 0. 1)

(2) 72.86 (reserve 2 significant figures)

Improve and expand

1. Which of the following statements is correct ( )

(A) The approximate number 28.0 is as accurate as the approximate number 28.00;

(B) The approximate number 0.32 has the same significant digits as the approximate number 0.302;

(C) The approximate number 2.4×10² is as accurate as the approximate number 240;

(D) Both the approximate number 230 and the approximate number 0.102 have three significant figures.

2. The approximate number 361 obtained by rounding, which of the following numbers cannot be the original number ( )

(A) 360.91 (B) 360.5 (C) 361.34 (D) 361.52

3. According to the requirements, use rounding method to get the approximate number and express it in scientific notation:

(1) 20549 (retain 3 significant figures)

(2) 0.0000000237 (accurate to 0.000000001)

Let’s summarize what we learned from this lesson!

1. Exact numbers and approximate numbers in life

2. Two forms of accuracy: to which digit; significant digits

3. Use rounding to approximate the number based on accuracy. Pay special attention to the flexible application of scientific notation when approximating large numbers or smaller numbers.

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Update Time: 2024-10-03

This template belongs to Mathematics courseware Hebei Education Edition Eighth Grade Mathematics Volume 1 industry PPT template

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