



 
Hi Loberto, Suppose the first term is $a$ and the common difference is $d$ then the first three terms are $a, a + d, a + 2d.$ If the third term is 10 more than the first term then $a + 2d = a + 10.$ Solving this gives $d = 5.$ Hence each term is $5$ more than the previous term and thus you already know that the fifth term is 15 more than the second term. You also know that the seventh term is 7 times the first term. What is the seventh term? This is 7 times the first term. What is $a?$ Penny  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 