sukhman wrote:Find a single discount equal to three consecutive discounts of 10%, 12% , 5 %

For these kinds of questions, it's useful to see the answer choices, since MANY GMAT questions can be answered quickly by using the answer choices to our advantage.

Here, it's useful to recognize that reducing a price by 10% is the same as multiplying the price by 90%
For example, reducing $40 by 10% is the same as finding 90% of $40.

Likewise, reducing a price by 12% is the same as multiplying the price by 88%.

And reducing a price by 5% is the same as multiplying the price by 95%.

So, if the original price is, say $100, then the final price after consecutive discounts of 10%, 12% and 5% is equal to $100(0.90)(0.88)(0.95)

NOTE: At this point, it's unlikely that we'd have to perform these tedious calculations (the GMAT is not designed to reward human calculators). Instead, we could use the answer choices to our advantage.

Having said that, $100(0.90)(0.88)(0.95) = $75.24

A price decrease from $100 to $75.24 represents a [spoiler]24.76%[/spoiler] discount.

Cheers,
Brent