Patterns, Sequences, Series and Logic
Sequences and series, patterns, repeating cycles, and the logic and flowcharts E3n names in its own description of the Algebra and Other Math sub-score.
5 topics · 20 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Patterns and Finding the Rule
- How it worksHow do you test a candidate rule against every term instead of just the first two?
- Worked exampleFind the next two terms of 3, 7, 15, 31, 63 and state the rule that builds them.
- Worked exampleWalk me through the pattern behind 1, 4, 9, 16, 25 and find its 12th term.
- Going furtherWhat changes about finding the rule when a pattern is built from dots and shapes instead of numbers?
Arithmetic Sequences
- How it worksHow does the common difference let you leap to the 50th term without writing out the first 49?
- Worked exampleFind the 40th term of 7, 11, 15, 19 using the common difference.
- Worked exampleWalk me through counting how many terms sit in the list 5, 9, 13, all the way up to 101.
- Common mistakeWhy isn't the 10th term of an arithmetic sequence just ten times the first term?
- Ties togetherHow does the common difference of a sequence show up as the slope of a line through its terms?
Geometric Sequences and Series
- How it worksHow does a common ratio push a sequence forward by multiplying and backward by dividing?
- Worked exampleFind the 7th term of 3, 6, 12, 24 and then the sum of all seven of those terms.
- Common mistakeWhy isn't 2, 6, 18 an arithmetic sequence when its gaps grow by a perfectly good rule?
- Going furtherWhat happens to a geometric sequence once the common ratio is a fraction such as 1/2?
Repeating Cycles and Remainders
- How it worksHow does dividing the position by the length of the cycle tell you where in the loop you land?
- Worked exampleFind the units digit of 3 raised to the 47th power using its four-step cycle.
- Worked exampleWalk me through finding the 100th letter in the endlessly repeating block A B C D E.
Logic and Flowcharts
- How it worksHow does a flowchart turn a rule full of branches into a single path you can walk?
- Worked exampleWalk me through a flowchart that doubles a number if it is even and adds 3 if it is odd, starting at 7.
- How it worksHow do two overlapping circles show which claims about two groups of people have to be true?
- Common mistakeWhy doesn't knowing the game was cancelled tell you it rained, when rain always cancels the game?
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