C = b-a a = 6 correct to the nearest integer
b = 15 correct to the nearest 5
Work out the upper bound for the value of C
Show your working clearly.

  C < 12

Step-by-step explanation:

The upper bound for C will be found where 'b' is a maximum and 'a' is a minimum.

The maximum that 'b' can be is half of the rounding value more than the reported value: 15 +5/2 = 17.5.

Similarly, the minimum 'a' can be is half the rounding value less than the reported value: 6 -1/2 = 5.5

Then the maximum value of C is ...

  C = 17.5 -5.5 = 12

The upper bound for the value of C is 12. (C < 12)

Additional comment

The minimum value of C will be (15 -5/2) -(6 +1/2) = 6. (6 < C). The value of C cannot actually be either of these values, since that would mean one of 'a' or 'b' would be rounded differently. It can only come close: 6 < C < 12.

from the figure we get,

the x axis shows   the months and,

the y-axis shows the number of satisfied customer.

each line or each cell in upward direction (y-axis) shows 500.

the appropriate scale for the y - axis is: -

a = 2000 customers

b = 4000 customers

c = 6000 customers

d = 8000 customers

e = 10000 customers

f = 12000 customers

g = 14000 customers