You need to add all the numbers from 10 to 99. You can do that quickly with the formula for an arithmetic series.
Chat with our AI personalities
105 is the sum
The smallest two-digit composite number is 10, which is the product of 2 and 5. The largest two-digit composite number is 99, which is the product of 3 and 33. To find the sum of the smallest and largest two-digit composite numbers, we add 10 and 99, resulting in 109.
All of the odd numbers between 11 and 99 inclusive are two digit numbers that are not multiples of 2. There are 45 of them.
For the tens digit to be a prime number then it must equal 2, 3, 5 or 7. There are four 3-digit prime numbers that fit the above condition and also have the tens and units digits forming a 2-digit prime number. 131, 137, 173, 179. The person supplying the question may like to sum the various combinations.
You can't write that as the sum of two prime numbers. Note: Goldbach's Conjecture (for expressing numbers as the sum of two prime numbers) applies to EVEN numbers.