Answer: 0.7
Locate the tenths place which is just to the right of the decimal point. We see a 6 in this spot. Just to the right of this 6 is the value 8. Since 8 is larger than 5, we bump the 6 up to 7 and erase everything else to the right. You can think of it like this
0.687 ---> 0.6 which bumps up to 0.7
This is like saying 687 is closer to 700 than it is to 600
