How many boys and girls in a school hall

[Johnx1]

There was an equal number of boys and girls in a school hall. After 108 boys left the hall, the number of girls in the hall became 4 times the number of boys in the hall. How many pupils were there in the hall at first?

my work:

Number of Boys = B
Number of Girls = G
G = B

We know that the number of girls was 4 times more after 108 boys left.

For boys:
-------------------------------------------------------
G = 4(b-108).
And since we know G = B

B = 4(B - 108)
B = 144.
------------------------------------------------------

For girls
-----------------------------------------------------
Then I plugged it back in G = 4(B - 108)

so, G = 4(144 - 108)
G = 4(36) = 144.
---------------------------------------------------

Total number of students is 144 + 144 = 288.

 

[Wilmer]

There was an equal number of boys and girls in a school hall. After 108 boys left the hall, the number of girls in the hall became 4 times the number of boys in the hall. How many pupils were there in the hall at first?

Correct! Good job...

Can be done quicker since B = G.
B - 108 = B / 4
4B - 432 = B
3B = 432
B = 144 : so 2B = 288