There were 90 more boys than girls at the swimming pool at first. After  of the girls and  of the boys left the pool, there were twice as many boys as girls who remained at the pool. How many boys were there at the swimming pool at first?

Let's denote the number of girls at the swimming pool at first as G. Then, the number of boys at the swimming pool at first is G + 90.

According to the problem, after some of the boys and girls left, there were twice as many boys as girls remaining at the pool. We know that 1/4 of the girls and 1/3 of the boys left, so the remaining number of girls is 3/4G and the remaining number of boys is 2/3(G + 90).

Setting up the equation according to the problem, we get:

2/3(G + 90) = 2 * 3/4G 2/3G + 60 = 3/2G 60 = 3/2G - 2/3G 60 = 9/6G - 4/6G 60 = 5/6G

Solving for G, we get:

G = 60 * 6/5 = 72

So, there were 72 girls at the swimming pool at first. Therefore, the number of boys at the swimming pool at first is G + 90 = 72 + 90 = 162.

Let's denote the number of girls at the swimming pool at first as G. Then, the number of boys at the swimming pool at first is G + 90.

According to the problem, after some of the boys and girls left, there were twice as many boys as girls remaining at the pool. We know that 1/4 of the girls and 1/3 of the boys left, so the remaining number of girls is 3/4G and the remaining number of boys is 2/3(G + 90).

Setting up the equation according to the problem, we get:

2/3(G + 90) = 2 * 3/4G 2/3G + 60 = 3/2G Solving this equation for G, we get:

60 = 3/2G - 2/3G 60 = 5/6G G = 60 * 6/5 = 72

So, there were 72 girls at the swimming pool at first. Therefore, the number of boys at the swimming pool at first is 72 + 90 = 162.