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Geekman

Guest

Help on problems concerning Cars and areas

May someone give me a explanation for 20 and 21`
My reasoning for 21
The whole area of the grid is 12 x 12, or 144.
If we want to find the area of the triangle it would be the grid - other space.
Other space = top left triangle(Area=18) + bottom left triangle(Area = 30), with the right rectangle having a area of 12 and the triangle bordering the rectangle 's area is 20. Add all of that together and you get 80. 144 - 80 = 64, but it is not there. ?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Help on problems concerning Cars and areas

Hi;

I like 48 for number 21.

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Grantingriver

Member

Registered: 2016-02-01

Posts: 129

Re: Help on problems concerning Cars and areas

20) If we let v1,v2 and v3 be the speeds of the car, bus and van respectively, and if t is the time when the car and van meet then we have:
680-[v1(2+t)+v3t]=0
680-[70(2+t)+65t]=0 ⇒ 680-140-70t-65t=0 ⇒ 540-135t=0 ⇒ t=540/135=4 hours
Now since the bus left town M at 1:30 pm that is 0.5 hours before the van then:
d1=4.5V2=405 miles ⇒ d2=d-d1⇒ d2=680-405=275 miles
Where d,d1 and d2 are the distance from towns M and N, the distance the bus traveled form town M when the car meet the van and the required distance respectively.

21) let us suppose that A1,A2,A3 and A4 is the areas of the square ODCE, the trangles OBA,BDC and ACE respectively. Where the points E and D have the coordinates (5,0) and (0,6) respectively. Then we have:
Area(ABC)=A1-(A2+A3+A4)=5×6×4_(3×2×3×2/2+3×2×5×2/2+6×2×2×2/2)=120-(18+30+24)=48 cm^2

Last edited by Grantingriver (2016-03-03 23:39:29)