In a consumer preferences survey, 20% respondents opted for product A whereas 60% opted for product B. The remaining individuals were undecided. If the difference between those who opted for product B and those who were undecided is 720, how many individuals had been interviewed for the survey?

Let the total number of individuals who had been interviewed for the survey = 'x'

Number of respondents who had opted for product A = 20% of x 

Number of respondents who had opted for product B = 60% of x

Number of respondents who had opted for none of the products = 20% of x ( remaining part out of 100%)

Difference between those who opted for product B and those who were undecided is 720.

$$\Rightarrow$$ (60% - 20%)x = 720 

$$\Rightarrow$$ 40% of x = 720 (or) x = 720 ($$\frac{100}{40}$$) (or) x = 1800

Hence, option B is the correct answer.