Math question and I need urgent help

Question

The speed of a river's current is 3 miles per hour. You travel 2 miles with the current and then return to where you started in a total time of 1.25 hours. What is your speed in still water?>Speed in still water:____ mi/h My second question is Brass is an alloy composed of 55% copper and 45% zinc by weight. You have 25 oz of copper and you want to determine how many oz of zinc you need to make brass. How much zinc do you need to use all of the copper and make the most amount of brass possible? a 21 oz b 30.6 oz c 24.3 oz d 25 oz e 20.3 oz f 20.1 oz g 20.45 oz Please show all your work. My last question is A car travels 120 miles in the same amount of time that it takes a truck to travel 100 miles. The car travels 10 miles per hour faster than the truck. Write and solve a proportion that relates the speeds of the vehicles. b. Speed of the car:____ mi/h Speed of truck:___ mi/h c. How long did the vehicles spend traveling? ____ hrs

Answer 1

1. Swimming in a River

You traveled 2 miles in 1.25 hours, which means that your speed relative to the shore is 2/1.25 mph. 2/1.25=8/5=1.4 mph.

Because you only achieved this speed after overcoming the speed of the current, you are swimming at 1.4+3 mph, so in still water you would be moving 4.4 mph.

2. Brass

I can find the amount of zinc by multiplying the amount of copper by 45/55. Do you see where I got those numbers? It's just one value divided by the other. Check it by evaluating 55X45/55=

It will also work when multiplying 25 oz times 45/55, which will very closely match one of your choices.

3. Car driving

There are lots of ways to use proportions, but they all rely on comparing ratios that we want to be equal. In this case, I think the simplest approach is a ratio of car:truck, or as a fraction car/truck.

We can compare the distances they both travel in the same amount of time: car/truck = 120/100

Or we can compare the speeds they are traveling. Since we don't know, I'll use r for the speed of the car:
car/truck=r/(r-10)

because car/truck should equal car/truck, it should also be true that 120/100=r/(r-10)

Cross-Multiply
120(r-10)=100r
120r-1200=100r
120r=100r+1200
20r=1200
r=60

If the car is going 60mph, how fast is the truck going?

How long would it take a car driving 60mph to travel 2 hours?
How long would it take the truck to drive 100 miles?

Let me know if you're lost and unable to finish these. Hope this helps!