Jeremy has 117 lawnmowers to service. He works on both gas and electric mowers. The ratio of electric mowers to gas mowers is 2 to 7. How many electric mowers does Jeremy need to service?

We solve the equations g + e = 117 and e / g = 2 / 7; where g = number of gas mowers and e = number of electric mowers;

So, g = 117 - e and 2g = 7e;

Then, 2 (117 - e) = 7e;

234 - 2e = 7e;

234 = 9e;

e = 234 : 9;

e = 26;

g = 117 - 26;

g = 91;