Question

a boy writes all the numbers from 100 to 999. the number of zeros that he uses is 'a', the number of 5's that he uses is 'b' and the number of 8's he uses is 'c'. what is the value of b + c – a?

Answer 1

The options for this question are missing:

A. 280

B. 380

C. 180

D. 80

The correct answer is option (B) 380

We can see by symmetry b=c and hence all we need to calculate b and a

b=280 and a=180

⇒ 2b−a= 380

Answer 2

Answer:

380

Step-by-step explanation:

if we think , then the numbers like 100, 200 300 are 9 in total then the zeroes in them are 9*2=18

now if we see numbers like 101 ,102, 103,201 are 9 in each set of 100 numbers. then in 9 sets the total zeroes are 9*9=81

then we come to numbers like 110 120 920 etc . so these numbers are 9 in each set of hundred then we have total zeroes are 9*9=81,

then in total number of zeroes are 81+81+18=180

now to count 5

if we conlude a number in ones place, are 105 205 125etc 10 per set so total are 9*10=90

5's in tens place lik 150 151 159 are 10 in each set so 10*9=90

now 5 in hundred place are fromm 500-599= 100 , so the total is 100+90+90=280

from this the the equation will be (2*280)-180=380