Doodles Do Algebra – Lesson 15


Update: This Lesson Is Part of Book 2 of Doodles Do Algebra: “Unknowns And The 29 Articles of Algebra” available on Amazon.


Teacher’s Notes:

Today DoodlePig walks your child through calculating something practical – how much money each of three boys gets from their father. The first half of the problem helps your child extract the mathematical relationships between the money each boy received and set up the problem to be solved. Then the second half of the main problem walks your child through solving the problem. At this point, the process of solving simple problems should be getting pretty easy for your child.


Available in the book, “Unknowns And The 29 Articles of Algebra, Book 2 of Doodles Do Algebra



1. first boy got x cents, second boy got x + 2 cents, third boy got x + 2 + 3 cents (since the third boy got 3 more cents than the second boy who got 2 more cents than the first boy), and all together the boys got 25 cents. So 3x + 7 = 25, and then 3x = 25 – 7, [intermediate steps here are first to subtract 7 from 25 to get 18, and then divide both sides of the equation by 3] and finally x=6. (just for completeness, boy 1 got 6 cents, boy 2 got 8 cents, and boy 3 got 11 cents).

2. 4 times 2x + 3 is 4 times 2x plus 4 times 3, as described a few lessons back. So the answer is 8x + 12.

3. This problem takes your child through the process of solving 5x-3 = 17. First you add three to both sides, and 5x = 20. Then you divide both sides by 5 and x=4.

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