If Tina swims 4 miles upstream at 1 mph and back downstream to the same point at 4 mph what is her average speed?

Her average speed is 1.6 miles per hour. Average speed is total distance covered by total time taken to do it. She swims 4 miles upstream, and at 1 mph, it takes 4 hours. She comes back downstream at 4 mph and so she covers the 4 miles in 1 hour. Her total mileage is 8 miles. It takes 4 + 1 hours or 5 hours to cover it. The 8 miles divided by 5 hours is 1 3/5 miles per hour, or 1.6 mph for an average speed.