How to find the total amount from given percentage

Question

I am trying to answer this question from internet for my mathematics practice.

What was the original price of an item if a discount of 20 percent

reduced the price to Rs.100? 

A. Rs.80 

B. Rs.120

C. Rs.125

D. Rs.150

E. Rs.250

How we can find its answer? What formula we can use and how we can solve it step by step, though it looks an easy question to me but I am out of touch for approximately 3 years

Thanks

Answer 1

If $x$ is the original price, $\displaystyle\frac{100-20}{100}x$ would reflect the price after a discount of 20 percent.

Answer 2

Suppose that the original price is Rs. 100 . Then the discount on the item be Rs. 20. And discounted price would be Rs.80.

So we can use unitary method , and find out. When the discounted price is 80 then original is 100. So if the discounted price be 100 , then original would be ?

$\dfrac{100 *100}{80}$

Answer 3

$$x-20\%x=100$$ $$x-\frac{20}{100}x=100$$ $$x-x/5=100$$ $$4x/5=100$$ $$x=500/4$$ $$x=125$$

Answer 4

$$x-20\%\cdot x=x-0.2x=\mathrm{rs}100$$ $$\mathrm{rs}100=80\%\cdot x$$ where $x$ is the total amount

So $x=\frac{\mathrm{rs}100}{80%}=\frac{\mathrm{rs}100}{0.8}=\boxed{\mathrm{rs}125}$

And to confirm: $\mathrm{rs}125-20\%\cdot\mathrm{rs}125=\mathrm{rs}125-0.2\cdot\mathrm{rs}125=\mathrm{rs}100$

Try and test it out.