How to calculate 10 * 7 / 15 =?

How to calculate 10 * 7 / 15 =?

10x7/15+2x7/3=14/3

Divide the items in the sequence an + 1 into (3) (5,7) (9,11,13) (15,17,19,21) (23), and then find the 100th bracket

Rule: all odd numbers start from the first, 2n + 1 (n ∈ n +), and there are n odd numbers in the nth bracket, then there are 1 + 2 +... + 99 = 99 × 100 / 2 = 4950 odd numbers in the first 99 brackets, and there are 100 odd numbers in the 100th bracket, starting from 2 × 4951 + 1 = 9903, until 2 × 5050 + 1 = 10101

There are two prime numbers whose sum is an odd number less than 100 and a multiple of 17. These two prime numbers are______ 、______ ．

Because the sum of two prime numbers is odd, one must be 2. There are three odd multiples of 17 less than 100, 17, 51 and 85. The difference between 17, 51 and 2 is not prime, so the other prime number is 85-2 = 83