Sampling & Comparing Data: 7th grade math in Fiji

Random samples, making predictions from a sample, and comparing two groups with centers and spreads.

Dive the soft coral capital of the world, sail between hundreds of islands and count the creatures of the reef. Characters here greet you with “Bula!” (hello in Fijian (it also wishes you life and good health)), and eggs hatch into hybrids of animals like reef manta ray, giant clam, green sea turtle and hawksbill sea turtle.

What your child practices

Follows Statistics & Probability — sampling and comparing populations (7.SP.A–B).

• Random and biased samples

  A sample represents a whole group when every member has the same chance to be picked and the sample is big enough.

  7.SP.A.1

• Predicting from a sample

  Use the fraction in a random sample to predict the count or percent in the whole group, and combine samples for a better estimate.

  7.SP.A.2

• Comparing two groups by their centers

  Find the mean or median of each random sample, then subtract to compare the two groups.

  7.SP.B.4

• Spread: range, IQR and mean absolute deviation

  Measure how spread out a sample is with the range, the interquartile range or the mean absolute deviation, and compare spreads.

  7.SP.B.3, 7.SP.B.4

• How far apart are two groups?

  Divide the gap between two means by the mean absolute deviation: the more spreads apart they are, the less the groups overlap.

  7.SP.B.3

Try a problem from Fiji

Every problem is a short story set in the world. These are real problems from the game. Kids get endless new ones with different numbers.

Common mistakes, and how to help

Every wrong answer in Mixmonde is planned: it points to a named mistake, and the tip after a miss explains it with that problem’s numbers. These are the mistakes this world watches for, grouped the way the grown-ups’ dashboard shows them.

• Graphs and data

  Reading graphs: missing that one picture stands for several, misreading the scale, or mixing up mean, median and range.

  Mistakes we catch: picked the easiest to reach, let people choose themselves, sampled only one part, sample too small, thought any sample works, thought you must check everyone, thought a bigger sample fixes bias, used only one sample, compared the totals, compared the largest values, did not put the data in order, gave the largest value, used the first and last values, gave the range, measured from the median, forgot to divide, gave the mean, used signed differences, divided by the wrong count, thought a bigger mean means more spread, ignored the mean absolute deviation, gave the gap only, divided one mean, divided by both spreads and ignored the spread.

  Try at home: Collect real numbers (bedtimes, scores) and find the mean, median and range together. Ask which one best describes “a typical day”.

• Ratio and scaling

  Adding when the situation multiplies: doubling a recipe by adding 2 to each amount, or taking a percent of the wrong total.

  Mistakes we catch: gave the sample count and divided but did not multiply.

  Try at home: Compare prices at the shop per item or per 100 g. For percents, always ask “percent of what?” and start from 10% and 1%.

• Reading the question

  The math works, but the answer is to a different question: a number already given, a halfway step, or only part of a two-step problem.

  Mistakes we catch: predicted the other part and gave one group’s center.

  Try at home: Underline what the question asks for and list the steps (“first find …, then …”). Tick each step off before giving the answer.

More Grade 7 worlds: Proportions & Percent · Rational Numbers · Expressions & Equations · Scale, Angles & Solids · Probability