Two groups of student, whose average ages are 20 years & 30 years, combine to form third group whose average age is 23 years. What is the ratio of the no. of students in the first group to the number of students in the second group? a) 7:3 b) 2:5 c) 5:2 d) 4:7
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Answer:
(15x+25y)/(x+y)= 23, or
15x+25y = 23x+23y, or
23x-15x = 25y-23y
8x=2y
x/y = 2/8 = 1/4
The first group has 4 times the number of students in the second group.
Check: Let x = 10 and y = 40.
So 10x+40y = (10*15 + 40*25]/(10+40) = (150+1000)/50 = 1150/50 = 23. Correct.
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