Data and Probability

Palengke prices: tracking the cost of ulam

Estadistika at probabilidad

Presyo sa palengke: pagsubaybay sa halaga ng ulam

Use a week of price monitoring from the public market to practise percentage change, averages and choosing the right measure of centre.

Where it fits

Data and Descriptive Statistics · Term 2 · Week 2
Earning Money and Percentages · Term 1 · Weeks 1–2

Competencies

gm11.t2.w2.c3 Identify the appropriate measure of central tendency and measures of variability of a given data set for different purposes.
gm11.t2.w2.c5 Interpret the computed measures of central tendency and variability.
gm11.t1.w1.c2 Apply a percentage increase or decrease in various contexts:

The data

Prevailing retail prices, one public market (₱ per kilo)
Commodity	Last month	This week	Change (%)
Well-milled rice	₱50	₱53	+6.0%
Red onion	₱150	₱190	+26.7%
Tomato	₱60	₱90	+50.0%
Galunggong	₱200	₱185	−7.5%
Chicken (whole)	₱190	₱195	+2.6%
Pork kasim	₱320	₱340	+6.3%
Eggs (per piece)	₱8.50	₱8.00	−5.9%

This week by Commodity

Source: Representative 2026 figures for classroom use; check current official rates before using for real decisions. Modelled on the Department of Agriculture's Bantay Presyo price monitoring format.

Scenario and worked example

Nanay's ₱500 budget

Engage

Every Sunday Nanay Cora buys a kilo each of rice, tomato, onion and galunggong with ₱500 and keeps the change for jeepney fare. After a typhoon, prices change as in the table. Does ₱500 still cover the basket? Which price change hurt most?

Worked example: percentage change

Explain

\%\text{ change} = \frac{\text{new} - \text{old}}{\text{old}} \times 100\%

\text{Onion: } \frac{190-150}{150}\times100\% \approx 26.7\%

Which average?

Elaborate

When one stall sells at a very different price, the mean is pulled toward it. The median (middle price) tells a shopper what a typical stall charges; the mode tells a vendor the most common price to match.

Collect your own data

Extend

Visit two stalls each; record prices of 5 commodities.
Compute class mean, median and mode per commodity.
Compare with the DA price watch for your region.

Discuss in class

Which commodity had the largest peso increase? The largest percentage increase? Why are they different?
If every price rose 10%, how would mean and median change?
Why do price-monitoring agencies report a 'prevailing' price rather than the mean?

Problems

5 problems · check your answer, then open the solution

Problem 1 Basic

Tomatoes rose from ₱60 per kilo to ₱90 per kilo after a typhoon. Find the percentage increase.

Your answer (%)
Show step-by-step solution
1. Increase: $90 - 60 = 30$ .
2. Percentage increase $= \dfrac{30}{60} \times 100\% = 50\%$ .
Answer: 50 %
Problem 2 Basic

Well-milled rice sells for ₱52, ₱54, ₱50, ₱56 and ₱53 per kilo in five stalls. Find the mean price.

Your answer (₱)
Show step-by-step solution
1. Sum: $52+54+50+56+53 = 265$ .
2. Mean $= 265 \div 5 = 53$ pesos per kilo.
Answer: 53 ₱
Problem 3 Standard

Red onion prices in five markets were ₱180, ₱200, ₱160, ₱220 and ₱190 per kilo. Find the median price.

Your answer (₱)
Show step-by-step solution
1. Order the values: 160, 180, 190, 200, 220.
2. The middle (third) value is 190, so the median is ₱190 per kilo.
Answer: 190 ₱
Problem 4 Standard

Galunggong prices in six markets: ₱180, ₱185, ₱190, ₱180, ₱175, ₱320. Which measure best describes the typical price, and why?

Choices a. Mean, because it uses every value b. Median, because one unusually high price pulls the mean up c. Mode, because ₱180 appears twice d. Range, because it shows the spread
Show step-by-step solution
1. Five prices cluster near ₱180–190; ₱320 is an outlier.
2. Mean $\approx 205$ is above every price except the outlier; median $= 182.5$ represents the typical stall.
Answer: b
Problem 5 Challenge Non-routine

A vendor buys cabbages at ₱45 per kilo, marks them up 30%, then gives a 10% discount to regular customers. What is the vendor's profit per kilo on a discounted sale, as a percentage of cost?

Your answer (%)
Show step-by-step solution
1. Marked-up price: $45 \times 1.30 = 58.50$ .
2. Discounted price: $58.50 \times 0.90 = 52.65$ .
3. Profit: $52.65 - 45 = 7.65$ ; as a percentage of cost $7.65/45 = 17\%$ .
4. Note that $+30\%$ then $-10\%$ is not $+20\%$ .
Answer: 17 %

Data tool (mean, median, charts) More practice: Data and Descriptive Statistics More practice: Earning Money and Percentages