Six bridges connect the islands shown. An explorer visits A, then B, then C, then D, and returns to A, crossing one connecting bridge on each leg. How many routes are possible?
On a field trip, class 5A is divided into groups of seven girls or four boys. Several whole groups line up. Which number cannot be the number of students in that line?
A store uses $\frac1{11}$ of its jars for macarons, then $\frac1{10}$ of the remaining jars for cookies. The remaining 18 jars hold jelly beans. How many jars are there in total?
Alice leaves home at 15:00 and cycles at 6 km/h, reaching her friend at 15:20. She stays 45 minutes, then cycles home along the same route at 8 km/h. When does she arrive home?
Seven students Alice, Ben, Cindy, Dan, Erik, Fred and Grace receive the seven scores in the chart, with names removed. Find Erik’s score. Alice and Grace differ by 1 point. Grace is 4 below Cindy; Cindy is 3 above Ben. Dan’s score is strictly between Ben’s and Fred’s. Cindy is either highest or lowest.
Peter finishes a mathematics book and an English book during the month. The table records his weekly pages. One quarter of the mathematics book is read in the final week. How many pages does the English book have?
A box has 6 red,8 green,10 blue,12 yellow and 15 white balls. Suzy draws without looking and without replacement. What is the minimum number that guarantees at least 3 red and at least 2 green balls?
The balanced hanging system contains four Moon boxes, two Earth boxes and a 20-kg weight. Find the mass of one Earth box. Treat the beams and strings as weightless.