Each boy contributed money equal to the number of girls and each girl contributed money equal to the number of boys in a class of 60 students. If the total contribution thus collected is Tk. 1,600, how many boys are there in the class?
A
30
B
25
C
50
D
20.5
Correct Answer: 30
Hints: ছেলেদের সংখ্যা x এবং মেয়েদের সংখ্যা y হলে x + y = 60................ (1) এবং, xy + xy = 2xy = 1600 xy = 800 তাহলে, x - y = √(x + y)2 - 4xy = √(60)2 - 4 × 800 x - y = 20............. (2) (1) and (2) no equation 2x = 60 + 20 2x = 80 x = 40