Math

You are right answer is 18 I also got 18

In first case area is 12000*4=48000m

2 person clear road at 3 hour so one person can do at 2*3 = 6 hour 

Than 10 person can do this same work at 6/10= .6hour =36 minutes

In second case area is 2000*12=24000

So by logic time to do this work is 18 min

2 snowplows can clear a road 12km x 4 m in 3 hours. How long will take for 10 snowplows to clear a road 2km x 12m.

 Hello Guest!

$N=W/t$

$N_{sp}=\dfrac{12km\cdot 4m}{2\cdot3h}\cdot \dfrac{1000m}{km}=8000m^2/h$

$t=\dfrac{W}{N_{sp}}$

$t=\dfrac{2km\cdot 12m}{10\cdot 8000m^2/h}\cdot \dfrac{1000m}{km}$

$t=0.3h\cdot\dfrac{60min}{h}=\color{blue}\ 18min$

10 snowplows clear a road of 2km x 12m in 18min.

You're right.

  !

2 snowplows can clear a road 12km x 4 m in 3 hours. How long will take for 10 snowplows to clear a road 2km x 12m.

My solution is 18 minutes but in book answer is 9 minutes. Am I wrong or there is error in book?

3 hr 2s / (12*4 km² )     *   2*12 km²/ 10s =  .3 hr        or       18 minutes 

Yep. I get .3 hours that’s 18 minutes.

I get 18 mins too

60/.3 = 18 so its 18 minutes

Wait I get 9 minutes Why am I getting 9 minutes when everyone else is getting 18 minutes

 I must have made a mistake

You made a mistake its 18 minutes I just rechecked my work. Its .3 hours that is 18 minutes.

Oh I did make a mistake. Its a good thing everyone is checking its easy to get wrong!!!

what are the amount and compound interest for $720 for 3 years at 5% per annum