Rational numbers: Class 8 maths video

0:00 Class 8 maths. Rational numbers.

0:03 Welcome aboard the Math Cruiser, hero!

0:06 I am Captain Calc, and today we are zooming into the world of rational numbers.

0:12 What is a Rational Number?.

0:14 A rational number is any number that can be written in the form p/q, where p and q are integers and q is not equal to 0.

0:23 Positive fractions, negative fractions, whole numbers, and zero are all rational numbers.

0:30 Try this one. Express -8 as a rational number in p/q form.

0:37 Any integer can be placed over 1.

0:40 Write -8 as -8/1.

0:44 So the answer is -8/1.

0:47 Properties of Rational Numbers.

0:50 The additive identity is 0 because adding 0 to any rational number leaves it unchanged.

0:56 The additive inverse of p/q is -p/q because their sum equals 0.

1:03 Try this one. Find the additive inverse of 5/9.

1:09 Change the sign of the number.

1:11 The additive inverse of 5/9 is -5/9.

1:16 So the answer is -5/9.

1:20 Operations on Rational Numbers.

1:23 To add or subtract rational numbers, find a common denominator first.

1:28 To multiply rational numbers, multiply top by top and bottom by bottom.

1:33 Try this one. Add: 1/4 + 2/3.

1:39 Find common denominator for 4 and 3, which is 12.

1:44 Convert fractions: 1/4 = 3/12 and 2/3 = 8/12.

1:51 Add numerators: 3/12 + 8/12 = 11/12.

1:58 So the answer is 11/12.

2:01 Rational Numbers on Number Line & Mean Method.

2:05 Rational numbers can be plotted between integers on a number line.

2:10 To find a rational number between two numbers a and b, calculate their mean: (a + b) / 2.

2:18 Try this one. Find a rational number halfway between 1/3 and 1/2.

2:25 Add the two numbers: 1/3 + 1/2 = 2/6 + 3/6 = 5/6.

2:34 Divide the sum by 2: (5/6) ÷ 2 = 5/12.

2:41 So the answer is 5/12.

2:44 Your turn. Write the numerator of the rational number -5/12. Pause the video, and try it.

2:54 The answer is -5.

2:57 Well done! Now try the practice and the quiz in this lesson on LearnFun.