The price of fuel decreases by 35%, 10% and 50% in three successive months, but increases by 40% in the fourth month. What is the percentage increase/decrease in the price of fuel in the fourth month as compared to its original price?

The correct option is Decreases by 59.05%.

Let the original price of the fuel be $P_0=100$ units.

We are given successive percentage changes in the price of fuel over four months:
- Month 1: Decreases by 35%
- Month 2: Decreases by 10%
- Month 3: Decreases by 50%
- Month 4: Increases by 40%

Let's calculate the price of the fuel step-by-step after each change.

Step 1: Price after the first month (35% decrease)
A decrease of 35% means the price becomes (100 - 35)% = 65% of its previous value.
$P_1=100\times (1-0.35)=100\times 0.65=65$

Step 2: Price after the second month (10% decrease)
A decrease of 10% means the price becomes (100 - 10)% = 90% of its previous value.
$P_2=65\times (1-0.10)=65\times 0.90=58.5$

Step 3: Price after the third month (50% decrease)
A decrease of 50% means the price becomes (100 - 50)% = 50% of its previous value.
$P_3=58.5\times (1-0.50)=58.5\times 0.50=29.25$

Step 4: Price after the fourth month (40% increase)
An increase of 40% means the price becomes (100 + 40)% = 140% of its previous value.
$P_4=29.25\times (1+0.40)=29.25\times 1.40=40.95$

Step 5: Calculate the overall percentage change
Compare the final price in the fourth month ($P_4=40.95$) to the original price ($P_0=100$):
$\text{Percentage Change}=\frac{P_4-P_0}{P_0}\times 100$
$\text{Percentage Change}=\frac{40.95-100}{100}\times 100=-59.05\%$

Since the resulting percentage change is negative, it indicates a decrease. Therefore, the price of fuel in the fourth month has decreased by 59.05% compared to its original price.