I need help in this question!!!
Question:
At a car park, 40% of the vehicles are cars. 90% of the remainder are vans and the rest are buses. There are 28 more vans than cars. After some cars have left, 20% of the remaining vehicles at the car park are cars. How many cars are there left at the carpark?

Jeslyn Lam wrote:
At a car park, 40% of the vehicles are cars. 90% of the remainder are vans and the rest are buses. There are 28 more vans than cars. After some cars have left, 20% of the remaining vehicles at the car park are cars. How many cars are there left at the carpark?
I think this question had been posted before and solution already given by someone but I could not locate it.

Suggested solution
Before
Cars : 40%
Vans : 90/100x60%=54%
Buses: 6%

Change
Only some cars left

After
Cars: 20%
Vans+Buses: 80%

At first,There are 28 more vans than cars.
54%-40%=14%
14% -> 28
1% -> 2
Number of cars at first -> 40% = 40x2=80
Number of vans+buses = 60% = 60x2=120

After some cars have left,number of vans+buses remained the same,
80%->120
1%-> 1.5
Number of cars in the end-> 20% = 20x1.5=30

Since the question is the no. of cars left in the end which is 20% the answer should be 30 cars.
Correct me if I am wrong.

At a car park, 40% of the vehicles are cars. 90% of the remainder are vans and the rest are buses. There are 28 more vans than cars. After some cars have left, 20% of the remaining vehicles at the car park are cars. How many cars are there left at the carpark?

A solution using Units rather than percentages.

We can use the Remainder Concept at first to find the number of cars, vans and buses. Then we can use External Unchanged to find the number of cars at the end.