relative error and percentage error

Question

the length and breadth of a rectangular object are 25.2 and 16.8cm respectively and have been measured to an accuracy of 0.1cm. The relative error and percentage error in the area of the object are ?

(please show the calculation part also)

Answer 1

Area = length * breadth = l * b

Relative error : dA/A = dl/l + db/b

dA/A = 0.1/25.2 + 0.1/16.8 = 0.00992

For percentage error multiply  by 100: 0.00992 * 100 = 0.992%

Answer 2

I'm unsure about this first part, but here goes...

 

The area is (25.2)(16.8) = 423.36, but we can only use three sigfigs, so the answer is 423. This indicates the accuracy of the area is 1 cm. This is the part I'm unsure about. But if the accuracy of the area is, indeed, 1 cm, then the following should be true:

 

Your absolute error is 1 cm

 

relative error = absolute area / actual value

relative area = 1 / 423

 

percentage error = relative area * 100 = 0.2%