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
After 4 years, the combined age of P and R will be 80 years. If their current age ratio is 7:5, find the age difference.
The Average age of 25 pupils in a class is ‘y’ years. If their principal, aged 50 years, joins them, the average rises by 1 year. Find the value of ...
A is 3 years older than B while C is 5 years younger than B. The ratio of age of A, 6 years hence and age of B, 5 years ago is 4:3. What was age of C, 8...
8 years ago, the ratio of the ages of Kim and Lee was 7:5. The present age of Ron is 15 years more than one-fourth of Lee’s present age. Find Ron's pr...
The total age of A, B and C eight years hence will be 98 years. Find the age of C three years hence, if the present age of A and B is 30 years and 25 ye...
- The age of Kiran 4 years ago was 10% more than the present age of Deepa. 4 years hence, the ratio of their ages will be 5:4. Find the difference between th...
The current average age of three friends, Aravi, Bipasa, and Chinu, is 24 years. The ratio of Chinu's and Diksha's present ages is 4:5, and Bipasa's cur...
Sum of the present ages of A, B, C and D is 54 years. After 3 years ratio of their ages is 4:3:2:2. What is C’s present age?
If the total ages of A and B is 12 years more than the total age of B and C. C is how many years younger than A?
A is younger than B by 3 years. If the ratio of A and B ages is 12:13 respectively, then find the age of A.
