Here we know that Margie is standing on a bridge looking at the river. She throws a rock over the bridge with an initial velocity of 60 ft/sec. The height, h, of the rock at the rime t seconds after it was thrown can be modeled by the equation:

$h(t) = -16t^2+60t+72$

To calculate how long will it take for the rock to reach the surface of the water, we need to set $h(t)=0$ . So:

$0 = -16t^2+60t+72 \\ \\ \\ \text{Using quadratic formula}: \\ \\ t=\frac{-b \pm \sqrt{b^2-4ac}}{2a} \\ \\ \\ a=-16 \\ \\ b=60 \\ \\ c=72 \\ \\ \\ t=\frac{-60 \pm \sqrt{60^2-4(-16)(72)}}{2(-16)} \\ \\ t=\frac{-60 \pm \sqrt{60^2-4(-16)(72)}}{2(-16)} \\ \\ t=\frac{-60 \pm \sqrt{8208}}{-32} \\ \\ t_{1}=4.70 \\ \\ t_{2}=-0.95$

Given that time can't be negative, we just choose the positive value. Therefore, <em>it will take 4.70 seconds for the rock to reach the surface water.</em>

6 0

2 years ago

An item that was selling for $80 is reduced to $42. Find the percent decrease in

Westkost [7]

Answer:

47.5%

Step-by-step explanation:

You have to first subtract 80 and 42 to find the decrease first. This is 38. Now, you have to divide this by the original number which is 80. So 38 divided by 80 is 0.475.

Now multiply this by 100.

You can easily move the decimal point to the right.

So you would get 47.5%

Hope this helped!

3 0

3 years ago