A boy writes all the numbers from 100 to 999. The number of zeroes that he uses is 'aa', the number of 5's that he uses is 'bb' and the number of 8's he uses is 'cc'.

What is the value of b+c−ab+c−a?

  • A.280
  • B.380
  • C.180
  • D.80

Answer: B

We can see by symmetry b=cb=c and hence all we need to calculate bb and aa

b=280 and a=180b=280 and a=180

⇒ 2b−a=2b−a= 380

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