Q:

Basic Math equation Question

I am finding it difficult to solve the following question, tried solving it by simultaneous equation method but the problem is the value of third equation is unknown. 
2 oranges, 3 bananas and 4 apples cost 15.
3 oranges, 2 bananas, and 1 apple costs 10.
What is the cost of 3 oranges, 3 bananas and 3 apples?

A:

Hint: You don't need to know the cost of a single orange or the cost of a single banana or the cost of a single apple in order to answer the question; you just need to know the cost of $3$ of each. Try adding together the first two equations and considering the ratio of each fruit's price.

A:

$\;\;\;\text{ 2 oranges, 3 bananas and 4 apples cost 15.}$
$\underline{ + \;\text{3 oranges, 2 bananas, and 1 apple costs 10.}}$
$=\text{5 oranges + 5 bananas + 5 apples costs }\;25.$
$\Rightarrow \text{1 orange + 1 banana + 1 apple costs}\;5.$
So $\; \text{(3 oranges + 3 bananas + 3 apples) costs }(3 \times 5).$

