Question

Josh rode his bike 11.4 miles. Claire rode her bike 6.8 miles. Which option explains how mental math can be used to find how much farther Josh rode than Claire? O A Round 11.4 to 11. Round 6.8 to 7. Then subtract 7 from 11 to get 4. Josh rode 4 miles farther than Claire O B. Add 0.2 to 6.8 to get 7. Subtract 7 from 11.4 to get 4.4. Then add 0.2 to 4.4 to get 4.6. Josh rode 4.6 miles farther than Claire. O C. Subtract 0.4 from 0.8 to get 0.4. Subtract 6 from 11 to get 5. Then add 0.4 to 5 to get 5.4. Josh rode 5.4 miles farther than Claire. O D. Round 11.4 to 11. Round 6.8 to 7. Then subtract 7 from 11 to get 4. Then add 0.4 and 0.8 to 4 to get 5.2. Josh rode 5.2 miles farther than Claire.

Answer 1

For this problem we want to find the easiest way to calculate how much farther Josh rode than Claire using mental math.

If we analyze the possibilities we know that the real difference is:

`11.4-6.8=4.6mi`

A Round 11.4 to 11. Round 6.8 to 7. Then subtract 7 from 11 to get 4. Josh rode 4 miles farther than Claire

For this case seems to be the easiest way but is not correct since the real answer is not 4.

B. Add 0.2 to 6.8 to get 7. Subtract 7 from 11.4 to get 4.4. Then add 0.2 to 4.4 to get 4.6. Josh rode 4.6 miles farther than Claire.

That seems the best option since we are adding two times 0.2 and in compensation we subtract the 0.4 from the decimal part of Josh

C. Subtract 0.4 from 0.8 to get 0.4. Subtract 6 from 11 to get 5. Then add 0.4 to 5 to get 5.4. Josh rode 5.4 miles farther than Claire.

The part when we add 0.4 after the procedure is not the correct one for this option

D. Round 11.4 to 11. Round 6.8 to 7. Then subtract 7 from 11 to get 4. Then add 0.4 and 0.8 to 4 to get 5.2. Josh rode 5.2 miles farther than Claire.​

For this case the rounding is not appropiate for the solution purposed