An equilateral triangle is subdivided into a number of smaller equilateral triangles, as shown. The shaded triangle has side length 2. What is the perimeter of the large triangle?
The number 25 can be written as the sum of three different primes less than 20. For instance, $25=5+7+13$.
How many multiples of 10 can be written as the sum of three different primes less than 20?
There are 10 children in a classroom. The ratio of boys to girls increases when another girl and another boy enter the room. What is the greatest number of boys that could have been in the room at the beginning?
A list of numbers has first term 2 and second term 5. The third term, and each term after this, is found by multiplying the two preceding terms together:
$$2,\ 5,\ 10,\ 50,\ 500,\ldots$$
The value of the eighth term is
Two sides of a regular hexagon are extended to create a small triangle.
Inside this triangle, a smaller regular hexagon is drawn, as shown.
In area, how many times bigger is the larger hexagon than the smaller hexagon?
The number $\dfrac{1\times2\times3\times4\times5\times6\times7\times8\times9\times10}{n}$ is a perfect square.
What is the smallest possible value of $n$?
In the triangle $ABC$ shown, $D$ is the midpoint of $AC$, $E$ is the midpoint of $BD$ and $F$ is the midpoint of $AE$.
If the area of triangle $BEF$ is 5, what is the area of triangle $ABC$?