How Many Boys Are in the Seventh Grade?Date: 05/20/99 at 15:52:20 From: Akj Subject: Word problem I can't do this word problem. My answer always comes out in decimal form and it's not supposed to: In a seventh grade of 360 students, 80 percent of all students can swim. 90 percent of the girls can swim, and 180 of the boys can swim. How many boys are in the seventh grade? Date: 05/22/99 at 14:48:49 From: Doctor Jeremiah Subject: Re: Word problem Hi there. The hard part of word problems is figuring out what equations the words mean. Let "b" be the total number of boys. Let "g" be the total number of girls. The boys and girls together make 360: b + g = 360 The total that can swim is the girls that can swim + the boys that can swim: 80% of 360 = 90% of g + 180 So now we have two equations and two unknowns (b and g): b + g = 360 0.80*360 = 0.90*g + 180 Solve the second one: 0.80*360 = 0.90*g + 180 288 = 0.90*g + 180 288 - 180 = 0.90*g + 180 - 180 108 = 0.90*g 108 = g*0.90 108/0.90 = g*0.90/0.90 120 = g*1 120 = g Now that we now "g" we can solve the first one: b + g = 360 b + g = 360 <== 120 = g b + 120 = 360 b + 120 - 120 = 360 - 120 b = 240 So there are 240 boys. Since you never got the right answer, do you know what went wrong? - Doctor Jeremiah, The Math Forum http://mathforum.org/dr.math/ |
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