Class 8 Mathematics - Rotational Symmetry

Rotational Symmetry

Swastika has a rotational symmetry (order:4)
image credits: wikipedia

Class 8 Mathematics 

A figure has rotational symmetry if the object can be rotated about a fixed point without changing the overall shape.

e.g. Consider the following equilateral triangle, if you rotate by 120°, you get the same figure.
Order of Rotational Symmetry
The order of rotational symmetry is the number of times the shape maps onto itself during a rotation of 360°.

Class 9 - Science - SOUND - Question Bank (#CBSENotes) (#CBSEClass9Notes)

SOUND

Question Bank

Question Bank based NCERT Class 9 Science Chapter on Sound.
Following questions have been asked in previous CBSE examination papers.


Q 1: Define frequency of a wave.

Q 2: Give a relation correlating sound velocity with its frequency and wavelength.

Q 3: What is SI unit of frequency?

Q 4: What is the true meaning of amplitude of a longitudinal wave?

Q 5: How is frequency of a wave related to its time period?

Q 6: On what factors does the loudness of a sound depend?

Q 7: Which sound has higher energy, a loud sound or a soft sound?

Q 8: On what factors does speed of sound in a medium depend?

Q 9: Define echo.

Class 9 - Mathematics - Ch10 - Circles (Worksheet) (#CBSENotes)

Circles 

CBSE Class 9 - Mathematics - Chapter 10

Worksheet 

Fill In the blanks

1. A _____ is a set of points in a plane, each one of which is at a constant distance from a fixed point in the plane.


2. A line segment joining two points on a circle is called the ______ of the circle.


3. A line which meets a circle in two points is called a ________ of the circle.


4. A chord passing through the center of the circle is called a ________ of the circle.

Class 10/9/8/7 - English Modal Verbs-Situations Table (#CBSENotes)

English Modal Verbs

Situations Table

Situation	Modal Verb	Example
requests (formal)	may	May I sit down?
requests (informal)	can	Can I sit down?
requests (polite)	would	Would you ind if I sit down?
permission (formal)	may	yoy may sit down
permission (informal)	can	You can sit down

Class 6/7/8/9/10 - संस्कृत - शब्द रूप (#cbsesanskrit) (#sanskrit)

शब्द रूप

संस्कृत

युष्मद् (तू)

Class 7 - Hindi - नीलकंठ - प्रश्न - उत्तर (भाग -२ ) - (#CBSENotes)

नीलकंठ 

नीलकंठ तुम नीले रहियो, दूध-भात का भोजन करियो, हमरी बात राम से कहियो'  

प्रश्न - उत्तर (भाग -२  )

प्र.१  जाली के बड़े घर में पहुँचने पर मोर के बच्चों का किस प्रकार स्वागत हुआ?

उत्तर- जाली के  बड़े घर में मोर के बच्चों के पहुँचते ही वहाँ हलचल मच गई। अन्य जीवों को वैसा ही कौतूहल हुआ जैसा नववधू के आगमन पर परिवार के बाकी सदस्यों में होता है।  लक्का कबूतर नाचना छोड़ कर दौड़ पड़े और उनके चारों और घूम-घूमकर गुटरगूँ करने लगे।  बड़े खरगोश गंभीर भाव से कतार में बैठकर उनका परीक्षण करने लगे।  छोटे खरगोश उनके आसपास उछलकूद मचाने  लगे।  तोते उनका निरीक्षण एक आँख बंद करके करने लगे।


प्र.२: लेखिका को नीलकंठ की कौन सी चेष्टाएँ बहुत भाती थी?

उत्तर- लेखिका को नीलकंठ का गर्दन ऊँची कर देखना, विशेष भंगिमा के साथ उसे नीची कर दाना चुगना और पानी पीना तथा गर्दन टेढ़ी कर शब्द सुनना आदि चेष्टाएँ बहुत भाती थी।  इनके अतिरिक्त पंखों को फैलाकर उसका नृत्य करना भी लेखिका को मोहित कर लेता था।

CBSE Class 9 - Mathematics - Probability - Problems and Solutions

Probability

Problems and Solutions (NCERT Exemplar Answers)

Problem 1: Two dice are thrown simultaneously 500 times. Each time the sum of numbers appearing on their top is noted and recorded as given in the following table:

Sum	2	3	4	5	6	7	8	9	10	11	12
Frequency	14	30	42	55	72	75	70	53	46	28	15

If the dice are thrown once more, what is the probability of getting a sum
(i) 3
(ii) more than 10
(iii) less than 5 or equal to 5
(iv) between 8 and 12

Solution: Click here to see the solution.


Problem 2: Here is an extract from a mortality table:

Age(in years)	60	61	62	63	64	65
Number of persons surviving out of sample of one million	16090	11490	8012	5448	3607	2320

(i) Based on this information, what is the probability of a person 'aged 60' of dying within a year?

(ii)What is the probability that a person 'aged 61'will live for 4 years?