Marcin buys 7 rulers and 15 crayons for £7. A ruler costs 12p more than a crayon.

Find the cost of one crayon.

28 p

Explanation:

To solve this problem we're going to use an equation. First let's write down the information that we do know.Let's use (r) for ruler and (c) for crayon.
So 7 rulers and 15 crayons cost £7 (or 700 pennies) --> 7r + 15c = 700But we also know that r = c +12
So we can substitute c + 12 into the first equation where r is at the moment.
7(c+12) + 15c = 700
Now let's expand the brackets. We multiply 7 by c to get 7c and 7x12 t0 get 84
7c + 84 +15c = 70022c + 84 = 700 Here I'm going to take 84 away from both sides. 22c = 616
Remember this is a non calculator paper so we need to find an easy way of dividing 616 by 22.
616 divided by 22 is 28 so c = 28Each crayon therefore costs 28p