Crate of bricks

Statement

A crate full of identical bricks has a mass of $95$ kg. Removing $3$ bricks drops the mass to $80$ kg. The empty crate has a mass of $5$ kg. How many bricks are left in the crate?

Solution

Mass of one brick. Removing $3$ bricks lowers the mass by $95-80=15$ kg, so each brick has mass $\frac{15}{3} = 5 \text{ kg}.$

Initial number. The crate alone weighs $5$ kg, so the bricks initially weigh $95-5=90$ kg. Let $n$ be their number: $5n = 90 \implies n = 18.$

After removing $3$ bricks, $18-3=15$ remain. Check: $15$ bricks weigh $75$ kg, plus $5$ kg of crate makes $80$ kg. Correct. $\boxed{15 \text{ bricks}}$