Question

800, increased by 50% and then decreased by 30%, yield what number?
A) 800
B) 760
C) 840
D) 820

Answer 1

Hint: Find the 50% of 800 by multiplying 800 with 50 and dividing by 100. Add the result to 800. Let the result after adding be x. Now find the 30% of x by multiplying x with 30 and dividing by 100. Subtract the result from the x. Let this result be y. y will be the required number.

Complete step-by-step answer:
We are given a number 800 that increases by 50%.
50% of 800 is
 $
  800 \times \dfrac{{50}}{{100}} \\
   = 800 \times \dfrac{1}{2} \\
   = 400 \\
  $
Therefore, 800 is increased by 50% means 400 is added to 800.
The final number will be $ 800 + 400 = 1200 $
Now the number 1200 has decreased by 30%.
30% of 1200 is
 $
  1200 \times \dfrac{{30}}{{100}} \\
   = 12 \times 30 \\
   = 360 \\
  $
Therefore, 1200 is decreased by 30% means 360 is subtracted from 1200.
The final number will be $ 1200 - 360 = 840 $
When 800 is increased by 50%, then the number 800 will become 1200.
When 1200 is decreased by 30%, then the number 1200 will be 840.
Therefore, from among the options Option C is correct, which is 840.
So, the correct answer is “Option C”.

Note: In mathematics, percentage is a ratio that represents a fraction with denominator 100. It is denoted using the percent sign ‘%’. 78% is equivalent to the decimal 0.78, or the fraction 78/100.Percentages is used as interest rates in banks, discounts in shopping malls and online websites.