To determine 80% of a number whose 20% is 90, follow these steps:
1. Find the full value of the number:
We know that 20% of the number is 90. To find the full value of the number, we set up the equation:
[tex]\[
\frac{20}{100} \times \text{Full Number} = 90
\][/tex]
Solving for the full number:
[tex]\[
0.2 \times \text{Full Number} = 90
\][/tex]
[tex]\[
\text{Full Number} = \frac{90}{0.2}
\][/tex]
[tex]\[
\text{Full Number} = 450
\][/tex]
2. Calculate 80% of the full value:
Now that we know the full value of the number is 450, we need to find 80% of 450. We do this by multiplying 450 by 80%, or 0.8:
[tex]\[
80\% \times 450 = 0.8 \times 450
\][/tex]
[tex]\[
0.8 \times 450 = 360
\][/tex]
Therefore, 80% of the number is \( \boxed{360} \).
Given the options:
a. 360
b. 72
c. 144
d. 225
The correct answer is [tex]\( a. 360 \)[/tex].
