If the price of an article increases by 49% and the sale of that article decreases by 21%, then what is the approximate effect on collection?

Correct option is C

Assume the original price is 100, and the original quantity sold is 100.

New price and quantity are:

New Price = 100 + 49 = 149
New Quantity = 100 - 21 = 79

Old and new collections are:
$$\text{Old Collection} = 100 \times 100 = 10{,}000$$

$$\text{New Collection} = 149 \times 79 = 11{,}771$$

Percentage change in collection is calculated as:

$$\text{Percentage change} = \frac{11{,}771 - 10{,}000}{10{,}000} \times 100 = 17.71\%$$

Short trick using net percentage change formula:
If one value increases by a% and another decreases by b%, use:

$$\text{Net effect (\%)} = a + b + \frac{a \times b}{100}= 49 + (-21) + \frac{49 \times (-21)}{100}= 28 - 10.29 = 17.71\%$$​​
So, the approximate effect on collection is an 18% increase.
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