Question

Bill wanted to try out different water craft he went 62 mikes downstream in a motor boat and 27 mikes down stream on a jest ski his speed on the jet ski was 10 mph faster than the motor boat bill spent a total of 4 hours on the water what was his speed in the motor boat

Answer 1

The speed on motorboat is 20 mph

Explanation:

here, we want to find the speed on the motorboat

if he has a speed of x mph on the motor boat, his speed on the ski will be (x + 10) mph

The total hours is 4 hours

Mathematically; speed = distance/time

Time on ski is 27/x+ 10

Time on motor boat is 62/x

The addition of both is 4

Thus;

27/(x + 10) + 62/x = 4

27(x) + 62(x + 10) = 4(x)(x + 10)

27x + 62x + 620 = 4(x^2 + 10x)

89x + 620 = 4x^2 + 40x

4x^2 -49x-620 = 0

using the quadratic formula;

{-b ± √(b^2-4ac)}/2a

where a = 4, b = -49 and c = -620

= 49 ± √(-49)^2-4(4)(-620)/8

So we have

49+ 111/8 or 49-111/8

Speed cannot be negative

(49 + 111)/8

= 20 mph