It costs Rs p each to send the first thousand messsages and Rs q to send each subsequent one If r is......

It costs Rs. p each to send the first thousand messsages and Rs. q to send each subsequent one . If r is greater than 1,000, how many Rupees will it cost to send r messages ?

We need to find the total cost to send r messsages, r > 1000.
The first 1000 messsages will cost Rs.p each (Or) 
The total cost of first 1000 messsages = Rs.1000p
The remaining (r - 1000) messsages will cost Rs.q each (Or)
The cost of the (r - 1000) = Rs.(r - 1000)y
Therefore, total cost = 1000p + rq - 1000q
= 1000(p - q) + qr

By: MIRZA SADDAM HUSSAIN