A lift has the capacity of 18 adults or 30 children. How many children can board the lift with 12 adults?

The correct option is 10.

To find out how many children can board the lift with 12 adults, we need to determine the equivalent capacity of adults in terms of children. Let us break this down step-by-step.

First, we are given the maximum capacity of the lift:
Capacity = 18 adults = 30 children

This relationship allows us to find the equivalent capacity of 1 adult in terms of children:
1 adult = $\frac{30}{18}$ children

Simplifying the fraction by dividing the numerator and the denominator by their greatest common divisor, which is 6, we get:
1 adult = $\frac{5}{3}$ children

We are given that 12 adults have already boarded the lift. Let us calculate the capacity consumed by these 12 adults in terms of children:
Capacity consumed = 12 × (capacity of 1 adult in terms of children)
Capacity consumed = 12 × $\frac{5}{3}$ children

Calculating this value:
Capacity consumed = 4 × 5 = 20 children

Now, we can find the remaining capacity of the lift in terms of children by subtracting the consumed capacity from the total capacity:
Remaining capacity = Total capacity in children - Capacity consumed in children
Remaining capacity = 30 - 20 = 10 children

Thus, 10 children can board the lift along with the 12 adults.