Mr Jones gave 30% of his salary to his parents. He spent $350 on food and 20% of the remaining money on transport. He saved the rest of his salary, which was $1120. What percentage of his salary did he spend on food?
if the salary was x, then we have
0.30x + 350 + 0.20(0.70x-350) + 1120 = x
x = $2500
or, in detail,
starting with $x, we have
parents: 0.30x, leaving 0.70x
food: 350, leaving 0.70x-350
transport: 0.20(0.70x-350) = 0.14x-70, leaving 0.56x-280
so now we have
0.56x-280 = 1120
x = $2500