Michi put $7.50 worth of gas in her car. Two co-workers who were riding to work with her offered to share the cost of the gas. One paid 1/2 of the total amount and the other paid 1/3 of the total amount. How much of the total amount was left for Michi to pay?
The two co-workers paid a total of 1/2 + 1/3 = 5 /6 of the total gas cost.
They paid a total of 5/6 * $7.50 = $<<5/6*7.5=6.25>>6.25.
Michi was left to pay $7.50 - $6.25 = $<<7.5-6.25=1.25>>1.25. Answer: \boxed{1.25}.