Why do we use the standard deviation as a measure of the uncertainty in single timing measurements rather than the rounding uncertainty on the timers themselves

Haruka hiked several kilometers in the morning. she hiked only 66 kilometers in the afternoon, which was 25% less than she had hiked in the morning. how many kilometers did haruka hike in all?

Bob the builder is making 480kg of cement mix. this is made by cement, sand and gravel in the ratio 1: 3: 4

What is the slope of the line that passes through the points (–9, 2) and (0, 4)? the slope of the line is