The average age of all students of class is 24 year. The average age of boys of the class is 29 year and that of girls is 20 year. If the number of girls in the class is 25, then find the number of boys in the class.
Answer: D Total age of girls = 20*25 =500year Total age of boys = 29*x = 29x (Where x is the number of boys). Average of whole class = (500+29x)/(25+x) = 24 => x= 20.
Q. No. 26:
There are 6 boys in the room. The ages(in years) of exactly three boys are prime numbers and ages(in years) of the other three boys are even numbers. If the ages(in years) of all the 6 students in the room are in A.P, then what is the average age(in years) of the boys in the room?
Answer: D Total cost of tyres = (100x - 3x2 +x3/3) Average cost of one tyre = 100 -3x + x2/3 Now, this is quadratic expression which at minimum value at x = -b/2a = 45.
Q. No. 28:
A box contains 85 nuts each of 100g and 94 bolts each of 150g. If the entire box with its contents weighs 42.5 kg, then what is the weight of the empty box ?