Examples
1) Akin is asked to add 20 to a number and then multiply by 4. Unfortunately, he did the opposite and first multiplied by 4 and then added 20. If he gets answer 104, what number did he start with and what should his original answer be?
Ans: Let us call the number n; so Akin did this. Multiply n by 4 = 4n, add 20 to give 4n + 20; So 4n + 20 = 104, If we take 20 away from each side, we get 4n + 20 - 20 = 104 - 20 or 4n = 84, (what number must I multiply by 4 to get 84 is the same as saying divide 84 by 4) So n = 84/4 = 21. He started with 21. The original answer should be add 20 to 21, 21 + 20 = 41, multiply by 4, 41 x 4 = 164. So the original answer is 164.
2) John had £66. He gave one third to his sister. How much does he have left?
Ans: John gave 1/3 of £ 66 or £22 to his sister. So he had £66 - £22 = £44 left.
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3) Find the angles x and y in the diagram below 
Ans: Angles in a triangle add up 180º so x + 95º + 35º = 180º or x + 130º = 180º ; x = 50º Angles on a straight line add up to 180º So y + x = 180º , x = 50º so y = 180º - 50º = 130º
More examples are on the blog.