1. The cost of buying some books is partly constant and partly varies with the number of books bought. The cost is #4800 when 20 books are bought and #8000 when 40 are bought. Find the cost when 1000 books are bought

Step-by-step explanation:

let the cost based on number of book bought be x and the constant be c:

4800 = 20x + c

8000 = 40x + c

c is common in both equations:

c =4800-20x

c = 8000-40x

equate the two:

4800-20x = 8000 - 40x

20x = 3200

x = 160

and c = 4800-20*160

c = 1600

Cost of 1000 books:

160*1000 + 1600

= 161600