Question

Harshini rode her bicycle 13.76 kilometers on Monday, 9.8 kilometers on Wednesday, and 16.415 kilometers on Friday.

She used the addition below to determine the total distance she rode over the three days.
13.76
9.8
+ 16.415
39.975
Which method determines whether her answer is reasonable?
Remove the decimal points and add 137 +98 + 16415 = 17,889; since 17,889 is not close to 39.975, her answer is
not reasonable.
Round all the numbers to 20; since 20 + 20 + 20 = 60 and 60 is not close to 39.975, her answer is not reasonable.
Round all the numbers to 10; since 10 + 10 + 10 = 30 and 30 is close to 39.975, her answer is reasonable.
Round 13.76 to 14, round 9.8 to 10, and round 16.415 to 16; since 14 + 10 + 16 = 40 and 40 is close to 39.975, her
answer is reasonable.

Answer 1

The last method (Round 13.76 to 14, round 9.8 to 10, and round 16.415 to 16; since 14 + 10 + 16 = 40 and 40 is close to 39.975, her answer is reasonable.)

Explanation:

Option 1 is unreasonable because removing the decimal points just changes the whole problem and claims that Harshini rode her bike 1376 kilometers on Monday and etc., which she did not. Option 2 is unreasonable because not all the numbers are near 20 and should be rounded to their nearest whole numbers instead to find a more accurate estimate. Option 3 is unreasonable for the same reason as option 2, the numbers should be rounded to their nearest whole numbers instead to find a more accurate estimate. Option 4 is reasonable because the numbers are rounded to the nearest whole numbers which makes the estimate more accurate.