Hey..
There can be 2 ways to solve this problem:
METHOD 1:
We know that 100gm costs Rs 20
Then 1kg = 1000gm
In 1000gm we can have 10 sets of 100gm
As each set costs Rs 20
Therefore the cost of 10 sets would be =
10*20 = Rs 200
METHOD 2:
We can calculate the cost per gm of chillies
100gm costs Rs 20
1 gm will cost = 20/100 = Rs 0.2
1 kg = 1000gm
Cost of 1000gm = 1000*0.2 = Rs 200
Hope this helps :)