Molly walked 3.45 miles on a hike. her sister walked 1.23 miles. her brother walked 0.85 miles. round each distance to the nearest tenth of a mile. about how much further did molly walk than her brother and sister combined?

3.45 rounded to the nearest tenth is 3.5.
1.23 rounded to the nearest tenth is 1.2.
0.85 rounded to the nearest tenth is 0.9.
To find how much further Molly walked than her brother and sister combined, you'd have to combine the amount of miles Molly's brother and sister walked:
1.2 + 0.9 = 2.1
Next, you would have to subtract Molly's amount of miles walked with the combination of her brother and sister's miles walked:
3.5 - 2.1 = 1.4
So, Molly walked 1.4 more miles on her hike than her brother and sister had walked combined.