The motor ship departed from pier A to pier B, the distance between which is 225 km. In 1.5 hours

The motor ship departed from pier A to pier B, the distance between which is 225 km. In 1.5 hours and, in order to arrive on time, increased the speed by 10 km per hour. Find the initial speed of the ship.

Let us denote by x km / h and (x + 10) km / h – the speed of the ship before and after the delay on the way.
Before the delay, he covered 1.5x km, after (225 – 1.5x) km. Now through the formula t = S / V:
225 / x = (225 – 1.5x) / (x + 10) + 3/2 + 1/2;
225x + 2250 = 225x – 1.5x ^ 2 + 2x ^ 2 + 20x;
225x + 2250 = 225x + 0.5x ^ 2 + 20x;
X ^ 2 + 40x – 4500 = 0;
D1 = 400 + 4500 = 4900 = 70 ^ 2;
X1 = – 90, x2 = 50,
since the speed cannot be a negative number, the initial speed is 50 km / h.
Answer: the initial speed of the ship is 50 km / h.