Acar moves with a speed of 40km/he for 15 minutes and then with a speed of 60km/hr for the next 15 minutes. find the total distance covered by the car

Explanation:

Let's break this into two parts, one for each speed.

40km/hr for 15 minutes.

Let's start with a simple  look.  How far would it go at this speed after 1 hour?  well, it's 40 km PER hour, so after an hour that's 40 km.  Since the speed is constant we know that cutting the time in half makes it go half the distance.  In this case 15 is 1/4 of an hour so it goes 1/4 of 40, or 10.

Another way to look at it is to remember the equation speed = distance divided by time.  or s = d/t.  Witht his you can just move the variables around to sole for them.  In this case we want to solve for distance, or d.  to do that multiply both sides.  

Pay attention to units though.  We want kilometers and hours, but 15 minutes is in minutes.  So we need to convert it.  Again, you could figure out 15 if 1/4 of 60, but another way is to use conversions.  1 hour is 60 minutes, so if you take 15 minutes and then multiply it by the fraction 1 hour/60 minutes, the minutes cancel out leaving you with 15*1/60 hours = 1/4 hours.

Now, looking at the speed times time to find distance we have 40 km/hour * 1/4 hours has the hours cancel out. so we have 40/4 km = 10 km.  Hopefully that  was easy enought o follow, I'll move through it more quickly for the next part.

60 km/hr for 15 minutes.  We want to cange minutes to hours so 15 min * 1 hour/60 minutes so the minutes cancel out to get 15/60 hours = 1/4 hours.  then since s = d/t, d = st.  so d = 60km/hr * 1/4 hr.  The hours cancel out so we get 60/4 km = 15 km.

The question was asking for total distance so we just add the two different parts.  that's 10 km and 15 km which gets us 25 km total.

Hopefully you were able to follow that, let me know if you have any questions though.  

d.7.5cm is your answer

i think the answer is a and b

i wish you luck