Question
If you write down all the numbers from 1 to 100, how
many times will you write the number 9?Solution
We’ll count how many times 9 appears in: Tens place Units place Tens place: Numbers like: 90, 91, 92, 93, 94, 95, 96, 97, 98, 99
That's 10 numbers with 9 in the tens place. → 10 occurrences Units place: Numbers ending in 9: 9, 19, 29, 39, 49, 59, 69, 79, 89, 99
→ 10 numbers with 9 in the units place → 10 occurrences So from 1 to 99, digit 9 appears = 10 (tens) + 10 (units) = 20 times
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