A sequence of numbers is formed by always adding the same number to get the next number in the sequence. The $10^{th}$~number in the sequence is $23$ and the $15^{th}$~number is $38$. What is the $12^{th}$~number? 
Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Arithmetic Sequences->Common Difference of an Arithmetic Sequence Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Arithmetic Sequences->Concepts of Arithmetic Sequences