In a survey 27 percent of the people choose salad over a meat dish. in all 81 people chose salads. how many people were in the survey

This means that the 81 people who chose salad were also equivalent to 27% % of all the people surveyed (let's call them "x")

so:

81=27%x
or

81=x

let's multiply both sides by 100:

8100=27x

and divide by 9:

900=3x

and by 3:
300=x

so we know that all the people surveyed numbered 300!

7.666270253x10 raised to the 18th power