A 3 cm wide border is printed on 100 sheet of paper ' each of length 40 cm and breadth 30 cm .if it coasts rupees 2.50 to print 100 Sq cm border what is the total cost of printing the border?

Answer :

We have : 3 cm wide border is printed on 100 sheet of paper ' each of length 40 cm and breadth 30 cm . , As :

Here AB  =  EF  = HG  =  DC  =  40 + 3 + 3 =  46 cm 
And
EH  =  IL =  JK  =  FG  =  30  - 3 - 3   =  24 cm
And
AE = EI  = JF  = FB  = KG  =  GC  = LH  =  HD  =  3 cm

So Area of printed border  =  Area of ABFE  +  Area of HGCD +  Area of EILH  +  Area of JFGK 

Area of printed border  =  46 $\times$ 3  +  46 $\times$ 3  +  24 $\times$ 3  + 24 $\times$ 3  =  138 + 138 + 72  + 72  =  420 cm²

So,

Total area of printed border in 100 sheets  =  420 $\times$ 100   =  42000 cm²

And

100 cm² of border cost  = Rs 2.5
So,
1 cm² of border cost  =  Rs . $\frac{2.5}{100}$
Therefore
42000 cm² of border cost  =  Rs . $\frac{2.5}{100}\times 42000 = 2.5 \times 420$ =  1050
So,

Total cost of printing border  =  Rs. 1050                                                                                 ( Ans )