There were 50 students who attended a summer camp and they were assigned to five rooms. The numbers of students are indicated in the diagram below. Find the value of $2A+3B+4C+5D+6E$, given that $A,B,C,D,E$ correspond to the number of students in each room.
In a bag, there are 3 green apples, 5 yellow apples, 7 green pears and 2 yellow pears. Simon randomly takes fruits out of the bag one by one. How many fruits must he take out in order to be sure that he has at least one apple and one pear of the same colour?
In a sale, each dress is reduced to 49% of its price and if two dresses are purchased at the same time, both are reduced to 45% of their prices. Lily buys two dresses together and pays 90 dollars for both. How many dollars has she saved compared to buying them separately?
Find the value of $3\boxtimes3$. The operation $\boxtimes$ is defined by:
(i) For all $x,y$, $x\boxtimes y=(x-1)\boxtimes(y-1)+x+y$.
(ii) For all $x$, $x\boxtimes1=1$.
Find a number which is under 100. Given that when this number is divided by 2, 3, 4 or 6, there is always a remainder of 1, but when divided by 7 there is no remainder.
Cut a cube by two planes parallel to the base of the cube into three rectangular blocks. The ratio of surface areas of these three blocks is 3:4:5. Find the ratio of their volumes in simplified form?
In the following figure, E is a point on side AD of the rectangle ABCD. Points F, G, H, and I are midpoints of CE, BF, CG and BH respectively. If the area of the triangle BCI is 1 cm², find the area of the rectangle ABCD in cm².