一群儿童被分在 A 礼堂和 B 礼堂两个礼堂里。A 礼堂里的儿童人数与 B 礼堂里的儿童人数之比为 3 : 8。在 A 礼堂中，男生人数与女生人数之比为 5 : 2。A 礼堂里有 18 名女生。求两个礼堂里的儿童总数。 答：___

1. Find the number of units representing girls in hall A and calculate the value of 1 unit.

In hall A, ratio of boys to girls is $5 : 2$.
Number of units for girls = $2$ units.
$2 \text{ units} = 18$
$1 \text{ unit} = 18 \div 2 = 9$

2. Find the total number of children in hall A.

Total units in hall A = $5 + 2 = 7$ units.
Total children in hall A = $7 \times 9 = 63$

3. Find the total number of children in both halls.

Ratio of children in hall A to hall B is $3 : 8$.
Total units for both halls = $3 + 8 = 11$ units.
Here, $3 \text{ parts} = 63$ children.
$1 \text{ part} = 63 \div 3 = 21$
Total children = $11 \times 21 = 231$