Level 2
In a scout camp, each scout was given either 2 or 4 wafers for supper. The ratio of the number of scouts to the number of wafers was 3 : 10. What fraction of the scouts received 2 wafers each?
Level 3
The average cost of some books is $75. When another 3 books are added, the total cost increases by $190. The average cost becomes $70. How many books are there in the end?
Level 3
The average cost of some books is $30.
When a book that costs $90 is added,
the average cost of the books becomes $40.
How many books are there in the end?