Duncan rode 2 kilometers on his bike. Harold rode twice as far as Duncan and Sara combined. How many kilometers did the three friends ride on their bikes all together? ( 1 kilometer=1000 meters)A.5km B.10km C.30km D.15 km

Total distance covered by all three friends is,

15 km assuming that Sara traveled a distance of 3 km.

30 km assuming that Sara traveled a distance of 8 km.

Step-by-step explanation:

Let D denotes the distance that Duncan covered on his bike.

Let H denotes the distance that Harold covered on his bike.

Let S denotes the distance that Sara covered on her bike.

Duncan rode 2 kilometers on his bike.

Mathematically,

D = 2 km

Harold rode twice as far as Duncan and Sara combined.

Mathematically,

H = 2(D + S)

H = 2(2 + S)

H = 4 + 2S

The distance covered by three friends all together is  

D + H + S

We don’t have enough information at this point to find out the total distance covered by all of them, so we need to assume the distance covered by Sara.

Assuming that Sara covered 0 km then

H = 4 + 2(0)

H = 4

Then total distance is

D + H + S

2 + 4 + 0

6 km

But 6 km doesn’t match any given option so try assuming another value for the distance covered by Sara.

Assuming that Sara covered 2 km then

H = 4 + 2(2)

H = 8

Then total distance is

D + H + S

2 + 8 + 2

12 km

But 12 km doesn’t match any given option so try assuming another value for the distance covered by Sara.

Assuming that Sara covered 3 km then

H = 4 + 2(3)

H = 10

Then total distance is

D + H + S

2 + 10 + 3

15 km

Assuming that Sara covered 8 km then

H = 4 + 2(8)

H = 20

Then total distance is

D + H + S

2 + 20 + 8

30 km

Therefore, the total distance covered by all three friends is,

15 km assuming that Sara traveled a distance of 3 km.

30 km assuming that Sara traveled a distance of 8 km.

b.) 160 miles on a 5 gallons car

step-by-step explanation:

240/10=24 miles/gallon

160/5=32 miles/gallon

30/1=30 miles/gallon

168/6= 28 miles/gallon

32 miles/gallon is the most amount, so this is the best.