Five sandwiches and four drinks cost £20. Two sandwiches and five drinks cost £8. Find the cost of one sandwich.

Aswimming pool had 2.5 million liters of water in it. some water evaporated, and then the pool only had 22 million liters of water in it. what percent of the water evaporated?

If sin(x) = 0 and cos(x) = 1, what is tan(x)?

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)