Smita04 wrote:
A typewriter can type digits at a speed of 5 digits per second. If it is used to type all the odd natural numbers till 1000 then how much time(in seconds) will be needed?
(a) 199
(b) 200
(c) 289
(d) 578
(d) None of these
Odd numbers which have only one digit: 1, 3, ..., 9 - a total of (9 - 1)/2 + 1 = 5 numbers
Odd numbers which have exactly two digits - 11, 13, ..., 99 - altogether (99 - 11)/2 + 1 = 45 numbers
Finally, odd numbers with exactly three digits - 101, 103, ..., 999 - a total of (999 - 101)/2 + 1 = 450 numbers.
The total number of digits is 5*1 + 45*2 + 450*3.
The time needed to type them (in seconds) is (5 + 45*2 + 450*3)/5 = 1 + 18 + 270 = 289.
Answer C.
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