Home › Solutions › USE and BSE › BSE › Real-life mathematics

Real-life mathematics

This page is part of the section “BSE. Real-life mathematics”. Here are solutions to practice-oriented problems: discounts and percentages, units of measurement, average speed, choosing the best tariff. All problems are written independently, with neat integer answers.

Problems with solutions

Problem 1. Percentage discount

A product cost 1200 rubles. The price was reduced by 15%. How much does the product cost now?

Find 15% of 1200 — this is the discount amount:

1200·15100=180
1200−180=1020

Answer: 1020 руб.

Problem 2. Units of measurement

How many grams are there in 2.5 kilograms?

There are 1000 grams in one kilogram. Multiply:

2.5·1000=2500

Answer: 2500 г.

Problem 3. Average speed

A car travelled 120 km in 2 hours. Find its average speed.

Average speed equals the distance divided by the time:

v= St = 1202 =60

Answer: 60 км/ч.

Problem 4. Choosing a tariff

A subscriber plans to use 200 minutes per month. Tariff A: 1.5 rubles per minute, no monthly fee. Tariff B: 300 rubles monthly fee plus 0.5 rubles per minute. Which tariff is cheaper and how much will it cost?

Cost of tariff A for 200 minutes:

200·1.5=300

Cost of tariff B for 200 minutes:

300+200·0.5=300+100=400

Compare: 300 < 400, so tariff A is cheaper.

Answer: Tariff A, 300 rubles.

Frequently asked questions

How to find the new price after a discount?

First find the discount amount: old price × percentage / 100. Then subtract the discount from the old price. For example, 1200 − 15% of 1200 = 1200 − 180 = 1020.

How to convert kilograms to grams?

Multiply the number of kilograms by 1000. For example, 2.5 kg = 2.5 · 1000 = 2500 g. Similarly: 1 t = 1000 kg, 1 km = 1000 m.

How to find the average speed?

Divide the total distance by the total time: v = S/t. For 120 km in 2 h: v = 60 km/h. Important: this works only if the motion was uniform over the whole segment.

How to choose the optimal tariff?

Calculate the cost of each tariff for your volume of services (minutes, gigabytes, etc.), then compare the results. Choose the tariff with the lowest cost for your consumption volume.

See also