A group of children is put into 2 halls, hall A and hall B. The ratio of the number of children in hall A to the number of children in hall B is 3 : 8. In hall A, the ratio of the number of boys to the number of girls is 5 : 2. There are 18 girls in hall A. Find the total number of children in both halls. Ans: ___

1. Find the number of boys in Hall A

Given the ratio of boys to girls in Hall A is $5 : 2$, and there are 18 girls in Hall A:
$2\text{ units} = 18$
$1\text{ unit} = 18 \div 2 = 9$
$\text{Number of boys} = 5 \times 9 = 45$

2. Find the total number of children in Hall A

$\text{Total in Hall A} = 45 + 18 = 63$ (or $7 \times 9 = 63$ children)

3. Find the total number of children in both halls

The ratio of children in Hall A to Hall B is $3 : 8$.
$3\text{ parts} = 63$
$1\text{ part} = 63 \div 3 = 21$
$\text{Total parts for both halls} = 3 + 8 = 11$
$\text{Total children} = 11 \times 21 = 198$