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Subject :IMO    Class : Class 4

Mary bought a new exercise book and she numbered all the pages. She wrote 151 digits in all. How many pages were there in the exercise book?

(A) 80

(B) 90

(C) 95

(D) 91

Ans 1:

Class : Class 4
ans a-80. From 1-9 there are 9 digits . so we are left with 151-9=142 digits. Note that from 10 onwards all numbers are of 2 digits. So there are 142/2=71 numbers to have 142 digits. Therefore there are 9+71=80 numbers.

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