The cost of an article is first decreased by 25% and then further decreased by 40%. Find the percentage change in the cost of the article.

Let the cost of the article be 100.

After a decrease of 25%, it becomes = 100 - 25% of 100

= $100 - \dfrac{25}{100} \times 100$

= $100 - \dfrac{2500}{100}$

= $100 - 25$

= 75

Now it is decreased by 40%, it becomes = 75 - 40 % of 75

= $75 - \dfrac{40}{100} \times 75$

= $75 - \dfrac{3,000}{100}$

= $75 - 30$

= 45

∴ Change on the whole = Final value - Initial value

= 45 - 100

= -55

Change on the whole is negative means change on the whole is decreasing.

∴ Percentage change = $\dfrac{\text{Change on the whole}}{\text{Initial value}} \times 100$ %

= $\dfrac{55}{100} \times 100$ %

= $\dfrac{5500}{100}$ %

= 55%

Hence, the cost of the article is decreased by 55%.