What can be the value of a single discount equivalent to a series of discounts of 10 percent, 15 percent and 25 percent?

The single equivalent discount is about 42.63%.

Successive discounts multiply the fraction: 0.90 x 0.85 x 0.75.

This equals 0.57375 of the marked price.

The amount paid is 57.375%, so the discount is 100% - 57.375%.

The single discount = 42.625%, which rounds to 42.63%.