Average - General QuestionsAverage - Important Formulas and Facts 1) Average = Sum of observations / Number of observations 2) Suppose an object covers a certain distance at 'a' kmph and an equal distance at 'b' kmph. Then the average speed during the whole journey = $\left(\frac{2ab}{a+b}\right)$
16.The average of six numbers is x and the average of three of these is y. If the average of the remaining three is z, then : A) x = y + z B) 2x = y + z C) x = 2y + 2z D) None of these View Answer Report DiscussAnswer: Option BExplanation:Clearly we have $x=\frac{3y+3z}{6} =>2x=y+z$
17.A car owner buys petrol at Rs 7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of petrol if he spends Rs. 4000 each year ? A) Rs. 7.98 B) Rs. 8 C) Rs. 8.50 D) Rs. 9 View Answer Report DiscussAnswer: Option AExplanation:Total quality of petrol consumed in 3 years = $(\frac{4000}{7.5}+\frac{4000}{8}+\frac{4000}{8.5})$$=4000(\frac{2}{15}+\frac{1}{8}+\frac{2}{17})=\frac{76700}{51}litres$Total amount spend =3x4000=12000.Average cost = $\frac{12000\times51}{76700}=\frac{6120}{767}=7.98$
18.The average weight of 16 boys in a class is 50.25 kgs and that of the remaining 8 boys is 45.15 kgs. Find the average weight of all the boys in the class. A) 47.55 kgs B) 48kgs C) 48.55 kgs D) 49.25 kgs View Answer Report DiscussAnswer: Option CExplanation:Required avrage = $\frac{50.25\times16+45.15\times8}{16+8}$$=\frac{804+361.20}{24}=\frac{1165.20}{24}=48.55$
19.If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55 and 60, then the average marks of all the students is : A) 53.33 B) 54.68 C) 55 D) None of these View Answer Report DiscussAnswer: Option BExplanation:Required avrage = $\frac{55\times50+60\times55}{55+60+45}$$=\frac{2750+3300+2700}{160}=\frac{8750}{160}=54.68$
20.A library has an average of 510 visitors on Sundays and 240 on other days. The average number of visitors per day in a month of 30 days beginning with a Sunday is : A) 250 B) 276 C) 280 D) 285 View Answer Report DiscussAnswer: Option DExplanation:Since the month begins with a sunday so there will be five sundays in the month .Required avearge = $\frac{510\times5+240\times25}{30}=\frac{8550}{30}=285$
