Use the formula for the nth term of an arithmetic sequence an = a1 + (n-1)d with n=10 a10 = a1 + (10-1)d a10 = a1 + 9d Substitute 75 for a10 75 = a1 + 9d 75 - a1 = 9d Since the right side is 9d, pick a number for a1 so that the left side will be a multiple of 9. You don't have to, but that's the way to avoid fractions. If we pick a1 to be 3, the left side will be 72 and that is divisible by 9. So let's pick a1 = 3 75 - 3 = 9d 72 = 9d 8 = d So substitute a1 = 3 and d = 8 in an = a1 + (n-1)d an = 3 + (n-1)(8) an = 3 + 8n-8 an = 8n - 5 <-- answer Then the sequence goes: 3,11,19,27,35,43,51,59,67,75,83,91,99,107,... Notice that the tenth term is 75. You could give other answers by choosing different numbers for a1. Edwin