Originally Posted by
scott4544
Please help me with the following problem. I can't figure it out. Thanks
A total of 270 students are in classes a and b. 30 Students moved into class b from a and then there was twice as many students in class b. Find the orginal number of students in classes a and b.
Off hand I would say 180 and 90. However, I don't know if this is right. Could you please help me? Thanks
Scott
This is how I see this problem.
A + B = 270 <- there are 270 students all together
B + 30 = 2B <- if you add 30 students to class B, there will be twice as many students in class B than before (in class B)
From that, we get that B = 30 and substituting it into the first formula, we get that A = 270 - 30 = 240
Then again, I'm not sure I understood the problem correctly... perhaps it was meant like this: If you move 30 students from class A into class B, then class B will have twice as many students as in class A (after the 30 students are moved)
That would give us a different formula:
B + 30 = 2*(A - 30)
Since we know that
A + B = 270 -> A = 270 - B
we can substitute that into first formula and get
B + 30 = 2*(270 - B - 30)
which means that
3B = 540 - 60 - 30 = 450 -> B = 150 -> A = 120
But perhaps I misunderstood the problem AGAIN! :) It's all about that sentence: "30 Students moved into class b from a and then there was twice as many students in class b". Twice as many as WHERE is the key.