Estimate how long it would take one person to mow a football field using an ordinary home lawn mower. Assume the mower moves with a 1 km/h speed, and has a 0.5m width.

I suggest that you convert the mower's speed to meters per hour, then multiply that speed by its width to get the area per hour that it can mow. Then divide that rate into the area of a football field in meters squared to get the number of hours it takes to mow. Post back with your work and we'll check it for you.

By the way - the area of a football field can vary. According to Wikipedia http://en.wikipedia.org/wiki/Footbal...eld_.28area.29

In many countries, an Association football pitch, or field, is used as a man-in-the-street unit of area It is necessarily restricted to order of magnitude comparisons by the fact that football pitches are officially allowed to measure between 100 and 110 m in length, and between 64 and 75 m in width; i.e. between 0.64 and 0.83 ha (1.6–2 ac).

An American football field, including both end zones, is 360 ft by 160 ft (ca. 110 x 49 m), or 57,600 square-feet (5,350 m², 0.54 ha, 1.32 acres). A Canadian football field is 65 yards wide and 110 yards long (ca. 101 x 59 m) with end zones adding a combined 40 yards to the length, making it 87,750 square-feet (8,156 m², 0.82 ha, 2.01 acres)

An Australian rules football field may be approximately 150 metres (or more) long goal to goal and 135 metres (or more) wide, although the field's elliptical nature reduces the its area to a certain extent. A 150 x 135 metre footy field has an area of approximately 1.6 ha (3.93 acres, 15,900 m²), twice the area of a Canadian football field and three times that of an American football field.