Work sheet: Subject – Maths, Class – VIII- Chapter: Direct and Inverse Variation 1. 68 boxes of contain commodity require a shelf- length of 13.6 m. How many boxes of the same commodity would occupy a shelf- length of 20.4m? 2. 11 men can dig 6 m long trench in one day. How many men should be employed for digging 27m long trench of the same type in one day? 3. 120 men had food provisions for 200 days. After 5 days, 30 men die due to an epidemic. How long will the remaining food last? 4. A car can finish a certain journey in 10 hours at the speed of 48km/hr. By how much should its speed be increased so that it may take only 8 hours to cover the same distance? 5. In a hostel of 50 girls, there are food provisions for 40 days. If 30 more girls join the hostel, how long will these provisions last? 6. A worker is paid Rs.210 for 6 days work. If his total income of the month is Rs. 875, for how many did he work? 7. A train 400m long is running at a speed of 72km/hr. How much time does it take to cross a telegraph post? 8. A train 360m long is running at a speed of 45 km/hr. What time will it take to cross a 140m long bridge? 9.A train 210m long took 12 seconds to pass a 90 m long tunnel. Find the speed of the train. 10. If 5men or 7women can earn Rs875per day, how much would 10men and 5women earn per day. 11. Q2. The cost of 16packets of salt, each weighing 900g, is Rs84. Find the cost of 27packets of salt, each weighing 1kg. 11. If 3persons can weave 168shawls in 14days, how many shawls will be woven by 8persons in 5days? 12. If the cost of transporting 160kgof goods for 125kmis Rs60. What will be the cost of transporting 200kg of goods for 400km? 13. 6oxen or 8cows can graze a field in 28days. How long would 9oxen and 2cows take to graze the same field? 14. 6 men working 8 hours a day, earn Rs 8400per week. What will be the earning per week of 9men who work for 6hoursa day? 15. A fort had provision for 300men for 90days. After 20days, 50men left the fort. How long would the food last at the same rate? 8th Direct _In direct variation with solved 2018-1
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Work sheet: Subject – Maths, Class – VIII- Chapter: Probability
1. If a dice is thrown. What is the probability of getting: (i) an odd number (ii) a multiple of 3 (iii) a perfect square numbers (iv) a number less than 4? 2. Three unbiased coins are tossed together. Find the probability of getting: (i) all heads (ii) two heads (iii) one head (iv)At least two head [ hint : Possible outcomes are HHH, HHT, HTH, HTT, THH, THT, TTH and TTT Ans: 1/8 , 3/8 , 3/8,1/2(HHH, HHT, HTH and THH)] 3. Find the probability that a leap year selected at random will contain 53 Sundays. [2/7] 4. One card is drawn from a pack of 52 cards, each of the 52 cards being equally likely to be drawn. Find the probability that the card drawn is : (i) an ace (ii) either red or king (iii) a face card (iv) a red face card) [Ans: 1/13, 7/13, 3/13,3/26] 5. Two dice are thrown simultaneously. Find the probability of getting: (i) a doublet i.e. same number on both dice. (ii) The sum as a prime number. [n=6 1/6,5/12] 6. If a die is thrown once, what is the probability of getting a prime number? 7. A coin is tossed 200times and tail is obtained 128 times. Now, if a coin is tossed at random, what is the probability of getting a tail? 8. In 100 throws of a dice, 5 is obtained 42 times. In a random throw, what is the probability of getting a 5? 9. A bag has 6 red balls and 8green balls. A ball is drawn from a bag without looking in to the bag. What is the probability of getting a green ball? 10. What is the probability of occurrence of an event? CBSE Chapter: Structure of an Atom IX Chemistry assignment
Q.1. What are Canal rays? Q.2. On the basis of Thomson’s model of an atom explain how the atom is neutral as a whole. Q.3 Draw a sketch of Bohr’s model of an atom with three shells. Q.4. Helium atom has atomic mass of 4u and has two protons in the nucleus. How many neutrons does it have? Q.5. If the K and L shells of an atom are full, then what would be the number of electrons in the atom? Q.6. If the number of electrons in an atom is 8 and the number of protons is also 8, then; (i) What would be the atomic number of the atom? (ii) What is the charge on the atom? Q.7. Na+ ion has completely filled k and L shells. Explain. Q.8. The average atomic mass of a sample of element X is 16.2 u. What are the percentages of isotopes 16 X8 and 18 X8 in the sample? Q.9. If Z=3, what would be the valency of the element ? Also, name the element. Q. 10. Composition of the nuclei of two atomic species X and Y are given as under X Y Protons = 6 6 Neutrons = 6 8 Give the mass numbers of X and Y. What is the relation between the two species ? Q.11. Why do the elements helium, neon and argon have zero valency ? Q.12. Why do elements which exist as isotopes have fractional atomic masses ? Q.13. Are mass number and atomic mass of an element equal in all respects? Q.14. The element ALuminium is written by the symbol 27 13 Al. Write the number of protons, electrons and neutrons present in it. Q.15. The electronic configuration of an element Z is 2, 8, 6. How many electrons does it require to have a stable configuration? Q.16. Two atoms A and B have the following composition: Atom A Atom B 17 protons 17 protons 18 neutrons 20 neutrons What are their mass numbers ? What is the relation between the species ?Q.17. The composition of two atomic particles is given : X Y Protons 8 8 Neutrons : 8 9 Electrons : 8 8 (i) What is the mass number of X ? (ii) What is the mass number of Y ? Q.18. Briefly describe the features of the Rutherford Model of an atom. what are the drawbacks ? Q.19. How do isotopes and isobars differ? Write three applications of isotopes. Q. 20. What observations in scattering experiment led Rutherford to make the following conclusions: (i) Most of the space in an atom is empty. (ii) Whole mass of an atom is present in its centre. (iii) Nucleus is positivity charged. Q.21. Explain why did Rutherford select a gold foil innhis alpha-ray scatering experiment. Q.22. The atom of an element ‘A’ has three electrons in the outermost shell. It loses one of these to the atom of another element ‘B’. What will be the nature and value of charge on the ion which results from ‘A’ Q.23.The atomic numbers of atoms of two elements are 18 and 20 respectively and their mass numbers are 40. What is the name that can be given to such pairs of atoms. Will they have same chemical characteristics? Q. 24. Give reasons for the following: (a) Isotopes of an element are chemically similar. (b) An atom is electrically neutral (c) Noble gases show least reactivity (d) Nucleus of an atom is heavy and positively charged. (e) Ions are more stable than atoms. Q.25. which of the two will be chemically more reactive; element X with atomic number 17 or element with atomic number 16 ? Further Study related link Solved Summative Assessment Paper Solved some important questions for coming CBSE Exam How was the neutron discovered? How was the proton discovered? How was the Electron discovered? Extra mark’s Notes, "Atomic Structure" How was the Nucleus discovered? Downloadable study material: JSUNIL TUTORIAL |
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