$30\%$ finish their job in $122\mathrm s$, $30\%$ finish their job in $68\mathrm s$, and $40\%$ finish their job in $190\mathrm s$. What is the average time it takes for a person to finish their job?
This is what I thought: $$\frac{122\times\frac3{10}x + 68\times\frac3{10}x + 190\times\frac4{10}x }x = 133$$
But I feel like it was a long time ago I did something like this so I don't know if it is correct.