Spinner designer

What the spinner designer does

Choose how many sections the spinner has, from 2 to 8, and give each color a size from 1 to 12 parts. The spinner redraws so every section's share of the circle matches its share of the total parts. The table shows each section's theoretical probability as a fraction in lowest terms and a percent. Then spin once, 10, 100 or 1,000 times: the table counts how often each color came up and gives its experimental probability.

Changing the design clears the counts, because a new spinner is a new experiment. New challenge asks you to design spinners that meet a rule, such as giving red a 1/2 chance or making blue three times as likely as yellow.

Why design your own

Coins and dice have equally likely outcomes, so students can come away thinking every probability is 1 over the number of outcomes. A spinner with unequal sections breaks that idea: there are three colors, but red can still have a 1/2 chance. Designing a spinner to fit a rule is probability in reverse, and it uses fractions, ratios and percents together. Spinning 1,000 times then tests the design.

Common mix-ups

• "Three colors means each has a 1/3 chance." Only if the sections are the same size.
• Using the size as the probability. A section of size 2 has a probability of 2 out of the total parts, not 2.
• Expecting 100 spins to match exactly. Experimental results vary and usually get closer with more spins.
• "Three times as likely" read as "three more parts". If yellow is 2 parts, blue must be 6.

A 10-minute spinner lesson

• Show the starting spinner. Ask for the chance of each color before looking at the table.
• Predict the number of reds in 100 spins, then spin 100 times.
• Press New challenge and solve it together, writing the fractions on the board.
• Spin 1,000 times to test the design.
• Ask: how could you design a spinner where yellow never wins? (You can't here; every section needs at least 1 part, but you could remove yellow.)

Where it fits by grade

• Grade 7: probability as a number from 0 to 1 (7.SP.C.5), long-run relative frequency (7.SP.C.6), and probability models that are uniform (7.SP.C.7a) or not uniform (7.SP.C.7b).
• Grade 6: practice fractions, ratios and percents (6.RP.A.3c) with the table.
• England: Key Stage 3 analyses the outcomes of experiments with equally and unequally likely outcomes, uses the 0 to 1 scale, and knows that the probabilities of all outcomes add to 1.

Learning more

Fractions, ratios and percentages are skills on Eurekami's skill map, and Daily Practice brings them back when they start to fade. For older students, Exam Prep includes GCSE Maths practice papers, and the AI tutor asks guiding questions when a probability problem is tricky.