Question

# 6 is 80% of what number?A) 6.5B) 7C) 7.5D) 8

Hint: First of all assume the number which we need to find, then take the 80% of it and equate the resultant to 6. We will just on simplification get the required number.

Assume the number which we are required to find be $x$.
So, we are given that: 80% of this number is 6.
Let us first find the 80% of the number $x$.
80% of the number $x$ will be $\dfrac{{80}}{{100}} \times x$ which is equal to $\dfrac{4}{5}x$.
Since, 80% of the number is given to be equal to 6.
Therefore, $\dfrac{4}{5}x = 6$
Cross multiplying to get the following expression:-
$\Rightarrow 4x = 6 \times 5$
Simplifying the multiplication on RHS, we will get:-
$\Rightarrow 4x = 30$
Taking the 4 from LHS to RHS, we will get:-
$\Rightarrow x = \dfrac{{30}}{4}$
Simplifying the RHS to get the following result:-
$\Rightarrow x = 7.5$

Hence, the correct option is (C).

Note: The students might make the mistake of taking 80% to the number 6 instead of letting the number required to be $x$. Percentage is the "result obtained by multiplying a quantity by a percent". So 10 percent of 50 apples is 5 apples: the 5 apples is the percentage. But in practice people use both words the same way.
A percentage is one way of writing a ratio; one can also write it as a fraction or decimal. There are ways to convert fractions to percentages or decimals to percentages.
Percentages are useful because people can compare things that are not out of the same number. For example, exam marks are often percentages, so people can compare them even if there are more questions on one exam paper than the other.