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The average marks of boys in a class is 52 and that of girls is 42. The average marks of boys and girls combined is 50. The percentage of boys in the class is
detailed solution
Correct option is A
Let n1 and n2 be the number of boys and girls respectively in the class.We have X1¯=52,X2¯=42 and X¯=50∴ X¯=n1X1¯+n2X2¯n1+n2⇒ 50=52n1+42n2n1+n2⇒8n2=2n1⇒n1=4n2∴ Percentage of boys =n1n1+n2×100=4n25n2×100=80Talk to our academic expert!
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An automobile driver travels from a plain to a hill station 120 km away at an average speed of 30 km per hour. He then makes the return trip at an average speed of 25 km per hour. He covers another 120 km on the plain at an average speed of 50 km per hour. His average speed (in km/hr) over the entire distance of 360 km will be
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