How many two digit prime numbers are there between 10 to 100 which remains prime numbers when the order of their digits is reversed?
9
A two-digit prime stays prime on digit reversal iff both digit-arrangements are prime. Checking all 21 two-digit primes:
\(11, 13\leftrightarrow 31, 17\leftrightarrow 71, 37\leftrightarrow 73, 79\leftrightarrow 97\) all qualify.
That gives the list \(\{11, 13, 17, 31, 37, 71, 73, 79, 97\}\) — exactly 9 numbers.
Similar Questions
The average of a set of 18 consecutive integers is 22.5. What is the largest integer in the set?
- The average of eleven consecutive positive integers is d. If the last two numbers are excluded, by how much will the average increase or decrease?
Three positive numbers are in the ratio 2 ∶ 3 ∶ 4. The sum of their squares is 2349. The average of the first two numbers is:
9435 is added to 7593, then 2607 subtracted from the sum. The result is divisible by:
The average of eight consecutive odd number is 28. The sum of the smallest and the largest number is:
If \(\frac{{45}}{{53}} = \frac{1}{{a + \frac{1}{{b + \frac{1}{{c - \frac{2}{5}}}}}}},\) where a, b and c are positive integers, then what is the value of (4a - b + 3c)
The numerator of fraction is 3 more than the denominator. When 5 is added to the numerator and 2 is subtracted from the denominator, the fraction becomes 8/3, When the original fraction is divided by \(5 \frac{1}{2}\) , the fraction so obtained is:
The denominator of a fraction is 4 more than the double of its numerator. When 3 is added to the numerator and 3 is subtracted from denominator the fraction becomes 2/3. Then find the difference between denominator and numerator of the original fration.
The sum of a non - zero number and twenty times its reciprocal is 9. What is the number?
Important Questions from Integers
Find the value of \(\sqrt{2025}\) .
How many times does the number 5 occur in the range of numbers from 1 to 100?
A. 21
B. 22
C. 20
D. 19
A prime number
A. is not a positive integer.
B. has no divisor at all.
C. has only 1 and itself as divisors.
D. has more than two divisors.
__________ are twin prime number.
A. (4, 9)
B. (2, 3)
C. (4, 6)
D. (3, 5)A factory produced 18,58,509 cassettes in the month of January, 7623 more cassettes in the of February and owing to short supply of electricity produced 25,838 less cassettes in March than in February. Find the total production in all?
A. 55,57,312
B. 59,83,245
C. 55,64,935
D. 56,08,988
