There were some boys and girls in the school hall at first. 40% of the boys and 10% of the girls left the school hall. As a result, 3/4 of the pupils remained in the school hall.There were 12 more girls than boys who remained in the school hall. how many boys were there at first?

.6b + .9g = 3/4 (b+g)

.9g = .6b + 12

Now just solve for b and g

THANK U SO.... MUCH

To find the number of boys at first, we need to follow these steps:

Step 1: Let's assume the total number of boys in the school hall at first is represented by 'B' and the total number of girls is represented by 'G'.
Step 2: We are given that 40% of the boys and 10% of the girls left the school hall, meaning 60% of the boys (0.6B) and 90% of the girls (0.9G) remained.
Step 3: We are also given that 3/4 of the pupils remained in the school hall, which means 3/4 of the total number of pupils at first (3/4 * (B + G)) remained.
Step 4: It is mentioned that there were 12 more girls than boys who remained in the school hall, so the equation becomes: 0.6B + 0.9G = 3/4 * (B + G) + 12.
Step 5: Simplify the equation: 0.6B + 0.9G = (3/4)B + (3/4)G + 12.
Step 6: Multiply every term in the equation by 4 to get rid of the fraction: 2.4B + 3.6G = 3B + 3G + 48.
Step 7: Simplify further: 2.4B - 3B = 3G - 3.6G + 48.
Step 8: Combine like terms: -0.6B = -0.6G + 48.
Step 9: Divide the equation by -0.6: B = G - 80.

Now we have an equation where the number of boys is expressed in terms of the number of girls. We need additional information to solve for the number of boys at first.