How many girls were there in the class?

[Johnx1]

There were 42 pupils in a class at first. After 6 boys left the class, there were 3 times as many girls as boys. How many girls were there in the class?

My answer: 42 = (x+ 6) + 3x
=> x = 9the (x+6) is basically (boys + 6)

So there are 27 girls and 9 boys? Did I do my work correctly?

 

[Greg]

I believe that's correct. Another equation we could use is 36 = 3(b - 6) + b - 6. Solving,

36 = 3b - 18 + b - 6
36 = 4b - 24
60 = 4b
b = 15

Then b - 6 = 9 and g = 27, so there are 27 girls in the class.

 

[HOI]

There were 42 pupils in a class at first. After 6 boys left the class, there were 3 times as many girls as boys. How many girls were there in the class?

My answer: 42 = (x+ 6) + 3x
=> x = 9the (x+6) is basically (boys + 6)

So there are 27 girls and 9 boys? Did I do my work correctly?

It's hard to tell because you start with an equation in "x" but have not said what "x" represents! I presume that you intended x to be the number of boys in the class after the first 6 boys left. The specific question was "How many girls were there in the class?" Yes, there were 27 girls. There were 9 boys left after the first 6 boys left so that there were intially 27 girls and 15 boys in the class. You can check that 27+ 15= 42, the number of students initially in the class.