The average age of Helen, Sharen, Claire and Donna is 20 years. Sharen is 8 years older than Helen and 15 years older than Claire. The sum of the ages of Helen and Sharen is 46, while that of Sharen and Claire is 39. What is Donna's age? Solution If we name each chca by its initial, from the statement we obtain the following equations: (H + S + C + D) / 4 = 20 S = H + 8 S = C + 15 H + S = 46 S + C = 39 If we solve the system we get that Donna is 22 years old.
Formerly, to move heavy objects several logs of similar size were used that were placed under the object to be moved. This was pushed and the trunks rolled so that the object moved forward. The drawing shows four identical trunks that have a circumference of 1 meter each.