2) Members of the ski club contributed equally to obtain $1800 for a holiday trip. When 6 members found that they could not go, their contributions were refunded and each remaining member then had to pay$10 more to raise the $1800. How many went on the trip? 3) Because of traffic Maria could average only 40 km/h for the first 20% of her trip, but she averaged 75 km/h for the whole trip. What was her average speed for the last 80% of her trip? 4) A number x is the harmonic mean of a and b if 1/x is the average of 1/a and 1/b. Find two positive numbers that differ by 12 and have harmonic mean 5 I don't know how to do these please help?? 2. Hello, Dunit0001! Here's #3 . . . 3) Because of traffic Maria could average only 40 km/h for the first 20% of her trip. But she averaged 75 km/h for the whole trip. What was her average speed for the last 80% of her trip? We know that: .$\displaystyle \text{Distance }\:=\:\text{Speed} \times \text{Time}$. . and its variations: .$\displaystyle \text{Time} \:=\:\frac{\text{Distance}}{\text{Speed}}\qquad\te xt{Speed} \:=\:\frac{\text{Distance}}{\text{Time}}$Suppose the trip was 400 km long. The first 20% is 80 km; the last 80% is 320 km. She drove 80 km at 40 kph. . . This took her: .$\displaystyle \frac{80\text{ km}}{40\text{ kph}} \:=\:2$hours. The she drove 320 km at$\displaystyle x$kph. . . This took her: .$\displaystyle \frac{320}{x}$hours. Then, to drive 400 km, her total time was: .$\displaystyle 2 + \frac{320}{x}$hours. Hence, her average speed was: .$\displaystyle \frac{400}{2 + \frac{320}{x}}$kph. Since her average speed was 75 kph, we have: .$\displaystyle \frac{400}{2 + \frac{320}{x}} \:=\:75$. . Now solve for$\displaystyle x.\$