Divisibility Rules of Important Numbers From 31 to 1000
Duration: 6 min
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This educational video provides a comprehensive overview of divisibility rules for various numbers, presented by an instructor from Knowledge Gate Eduventures. The lecture begins with a title slide and a colorful, circular diagram summarizing rules for divisors 2 through 10. The main content consists of a detailed table that systematically lists divisibility rules for divisors from 31 to 99. For each divisor, the video explains a specific condition, such as 'Subtract three times the last digit from the rest' for 31, and provides a worked example. The instructor uses a digital whiteboard to demonstrate the application of these rules, for instance, showing how to test 837 for divisibility by 31. The video concludes with a final slide that thanks the viewer, summarizing the extensive list of rules covered.
Chapters
0:00 – 2:00 00:00-02:00
The video opens with a title slide displaying 'DIVISIBILITY RULES' over a background of scattered numbers. This transitions to a colorful, hand-drawn circular diagram that visually organizes divisibility rules for divisors 2 through 10, with examples like '2: (is an even number)' and '3: the sum of the digits is divisible by 3'. The instructor, Yash Jain Sir, appears in a small window, introducing the topic. The scene then shifts to a digital whiteboard where the instructor begins writing, starting with the number 31 and the word 'prime', setting the stage for the detailed rules to follow.
2:00 – 5:00 02:00-05:00
The video presents a detailed table of divisibility rules. The instructor explains the rule for 31: 'Subtract three times the last digit from the rest', demonstrated with the example 837, where 83 - (3x7) = 62. The rule for 32 is shown as 'The number formed by the last five digits is divisible by 32', with an example of 25,135,520. The rule for 33 is 'Add 10 times the last digit to the rest', illustrated with 627, where 62 + (10x7) = 132. The instructor continues to explain the rule for 35: 'It is divisible by 3 and by 11', using the example 627, where the sum of digits (6+2+7=15) is divisible by 3, and the alternating sum (6-2+7=11) is divisible by 11. The table also shows rules for 37, 39, and 41, with the instructor explaining the rule for 41: 'Sum the digits in blocks of five from right to left', using 72,841,536,727 as an example.
5:00 – 6:03 05:00-06:03
The video continues with the table of divisibility rules, showing the rule for 43: 'Add 13 times the last digit to the rest', with the example 3629, where 362 + (13x9) = 3741. The rule for 47 is 'Subtract 14 times the last digit from the rest', demonstrated with 1,642,979, where 1,642,97 - (14x9) = 16403. The rule for 49 is 'Add 5 times the last digit to the rest', shown with 705, where 70 + (5x5) = 95. The video then shows the rule for 51: 'Number must be divisible by 3 and 17', with the example 459, where 4+5+9=18 is divisible by 3, and 45-9=36 is divisible by 17. The final rule shown is for 99: 'Number is divisible by 9 and 11', with the example 891, where 8+9+1=18 is divisible by 9, and 8-9+1=0 is divisible by 11. The video ends with a 'THANKS FOR WATCHING' slide.
The video systematically teaches a series of advanced divisibility rules, moving from a general overview to a detailed, table-based presentation. The core teaching method involves a clear, structured table that pairs each divisor with a specific, often non-intuitive, rule and a concrete example. The instructor's use of a digital whiteboard to demonstrate the application of these rules, such as the step-by-step calculation for 837 ÷ 31, reinforces the practical application of the concepts. The progression from simpler rules (like 2, 3, 5) to more complex ones (like 31, 43, 99) provides a logical learning path, culminating in a comprehensive reference guide for divisibility testing.