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Secondary 1 · Mathematics
Numbers · Integers

Problems with Integers

You have $\text{RD}\$45$ in your account, the thermometer in Constanza reads −2 °C, the elevator in the building goes down to the basement, and the Zona Colonial was founded centuries ago, in a year that is counted backward. All these problems look alike: there is a starting point and a series of moves, positive or negative, that have to be combined in order. How do you set them up without getting tangled?

Money and temperatures

When you deposit money, the amount goes up. When you pay, it goes down. If you owe money, your balance is negative. Temperature works the same way: it rises or falls, and it can end up below zero (in Constanza, on winter mornings).

Balance diagram with a starting value of 45 pesos and four successive moves that give a final balance of 35 pesos. Starting balance: 45 pesos −12 pesos +20 pesos −15 pesos −3 pesos 45 − 12 + 20 − 15 − 3 = 35 pesos
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Salma has $\text{RD\$}\ 34$ in her money box. She decides to buy a book that costs $\text{RD\$}\ 15$ and a backpack that costs $\text{RD\$}\ 25…

Salma has $\text{RD\$}\ 34$ in her money box. She decides to buy a book that costs $\text{RD\$}\ 15$ and a backpack that costs $\text{RD\$}\ 25$. As she does not have enough money, her parents tell her she can owe them the remainder. What integer represents Salma's final balance with respect to her parents?

Solve
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In a video game tournament, "The Gamers" team has a total of $-150$ points accumulated for committing fouls. If in the final round they get a bonus of $225$ points, how…

In a video game tournament, "The Gamers" team has a total of $-150$ points accumulated for committing fouls. If in the final round they get a bonus of $225$ points, how many points do they have on their scoreboard now?

Solve
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Marta has $\text{RD\$}\ 45$ in her bank account. Over the weekend, she makes the following transactions: she pays for a streaming platform subscription for $\text{RD\…

Marta has $\text{RD\$}\ 45$ in her bank account. Over the weekend, she makes the following transactions: she pays for a streaming platform subscription for $\text{RD\$}\ 12$, receives a bank transfer (Bizum) of $\text{RD\$}\ 20$ from her father and buys a book costing $\text{RD\$}\ 15$. If at the end of Sunday her bank charges her an account maintenance fee of $\text{RD\$}\ 3$, what is the final balance of her account?

RD$0 RD$10 RD$20 RD$30 RD$40 RD$50 RD$60 +RD$45 −RD$12 +RD$20 −RD$15 −RD$3 ?RD$ Start TV series Bizum Book Fee Balance
Solve

Floors, heights, and depths

Elevators, divers, and drones move "up" (positive) or "down" (negative) from a level $0$. Sea level is $0$: Pico Duarte is in positive territory, and the ocean floor or Lago Enriquillo is in negative. In a building, the first level is $0$ and the basements are $-1$, $-2$, $-3$…

Vertical axis with sea level at zero, a peak at 1,200 meters and a cave at minus 85 meters, with the distance between them. sea level (0) peak: +1,200 m cave: −85 m distance = |1,200 − (−85)| = 1,285 m
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A food delivery driver enters the elevator of a large shopping center on the third basement floor, which is shown as floor $-3$. First, they go up $7$ floors to deliver…

A food delivery driver enters the elevator of a large shopping center on the third basement floor, which is shown as floor $-3$. First, they go up $7$ floors to deliver an order and, immediately afterwards, go down $2$ floors to pick up another order. Which floor is the delivery driver on after these movements?

+5 +4 +3 +2 +1 0 −1 −2 −3 −4 Goes up 7 Goes down 2 Start End
Solve
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A diver is submerged in the ocean at a depth of $18$ meters below sea level ($-18\ m$). If he ascends $7$ meters to observe a coral reef and then descends another $4$…

A diver is submerged in the ocean at a depth of $18$ meters below sea level ($-18\ m$). If he ascends $7$ meters to observe a coral reef and then descends another $4$ meters, at what depth is he finally? Express the result as an integer.

Sea level (0 m) 0 −10 −20 −18 +7 m −4 m ? ?
Solve
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The highest peak of a volcanic island is located $1\ 200$ meters above sea level. On the same island, there is an underwater cave whose base is $85$ meters below sea…

The highest peak of a volcanic island is located $1\ 200$ meters above sea level. On the same island, there is an underwater cave whose base is $85$ meters below sea level. What is the difference in height between the top of the peak and the base of the cave?

Sea level Peak Cave base 1.200 m 85 m 0 m ?
Solve
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A diver exploring a coral reef is $14$ meters below sea level. If he decides to descend another $18$ meters to observe some archaeological remains and then climbs $9$…

A diver exploring a coral reef is $14$ meters below sea level. If he decides to descend another $18$ meters to observe some archaeological remains and then climbs $9$ meters to get closer to the surface, at what depth is he now? Represent the situation using integers.

Solve

Dates before and after Christ

Year $0$ (approximately) separates the BC years (which are treated as negative; the larger the number, the older) from the AD years (positive).

Timeline with year zero in the center, 570 BC as a negative number on the left, and 415 AD as a positive number on the right. 0 570 a. C.→ −570 415 d. C.→ +415 before Christ: negativesafter: positives
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A historian is studying the life of an Ancient Greek sculptor. According to records, the sculptor was born in $495$ BC and died in $429$ BC. How many years did this…

A historian is studying the life of an Ancient Greek sculptor. According to records, the sculptor was born in $495$ BC and died in $429$ BC. How many years did this sculptor live?

Solve
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Pythagoras, the famous Greek mathematician and philosopher, was born in $570$ BC and died in $495$ BC. At what age did Pythagoras die? Use integers (associating years BC…

Pythagoras, the famous Greek mathematician and philosopher, was born in $570$ BC and died in $495$ BC. At what age did Pythagoras die? Use integers (associating years BC with negative numbers) to carry out the calculation.

Towards year 0 ➔ −600 −550 −500 −570 Birth −495 Death Age?
Solve
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The Greek philosopher Hypatia of Alexandria died in the year $415$ AD at the age of $45$. Her father, Theon of Alexandria, was a famous mathematician who was born $80$…

The Greek philosopher Hypatia of Alexandria died in the year $415$ AD at the age of $45$. Her father, Theon of Alexandria, was a famous mathematician who was born $80$ years before she died.

  1. a) In which year was Hypatia born? (Express it as an integer).
  2. b) In which year was her father Theon born?
  3. c) How old was Theon when his daughter was born?
Solve

Multi-step problems

Long problems chain together several moves, sometimes with multiplications, divisions, or points that are won and lost. It helps to write down the partial result after each step. If there are several different operations, remember the order of operations: first multiplications and divisions, then additions and subtractions.

Diagram of the levels of a building with successive moves from level zero down to level minus ten. start0 up 12+12 down 15−3 up 7+4 down 14final result: −10
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At a weather station in Valle Nuevo, the thermometer read a temperature of -6^° C at 8:00 in the morning. By 12:00 noon, the temperature had risen by 9^° C, and by 20:00…

At a weather station in Valle Nuevo, the thermometer read a temperature of -6^° C at 8:00 in the morning. By 12:00 noon, the temperature had risen by 9^° C, and by 20:00 in the evening it had fallen by 7^° C compared to noon. What temperature did the thermometer read at the end of the day?

0ºC Temp +10 +5 0 −5 −10 8:00 −6ºC +9ºC 12:00 +3ºC −7ºC 20:00 (End) −4ºC
Solve
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An Amazon delivery driver starts their workday on floor $3$ of a large logistics center. First, they go down $5$ floors to pick up a package in the basement, then go up…

An Amazon delivery driver starts their workday on floor $3$ of a large logistics center. First, they go down $5$ floors to pick up a package in the basement, then go up $7$ floors to deliver it to an office and, finally, go down another $3$ floors to rest in the cafeteria. Which floor is the cafeteria on? Express the result as an integer.

Solve
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In a board game, you gain $15$ points for each correct answer, but you lose $8$ points for each wrong answer and $4$ points for each question left unanswered. If out of…

In a board game, you gain $15$ points for each correct answer, but you lose $8$ points for each wrong answer and $4$ points for each question left unanswered. If out of a total of $20$ questions you got $12$ correct, $5$ wrong, and left the rest unanswered, what is your final score?

Solve
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A scientist is carrying out a chemical experiment. They place a compound in a special freezer that lowers the temperature of the sample by $4^\circ C$ every hour. If the…

A scientist is carrying out a chemical experiment. They place a compound in a special freezer that lowers the temperature of the sample by $4^\circ C$ every hour. If the sample was initially at a room temperature of $18^\circ C$, what temperature will the sample be after $6$ hours? Express the result using a single calculation combining integers.

Solve
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In a scientific laboratory, an experiment is being conducted with a gaseous substance. The initial temperature of the sample is $12$ ºC below zero. The process follows…

In a scientific laboratory, an experiment is being conducted with a gaseous substance. The initial temperature of the sample is $12$ ºC below zero. The process follows these stages:

  1. During the first $5$ minutes, the temperature drops by $3$ ºC each minute.

  2. Then, it is placed in a heating chamber where the temperature rises by $48$ ºC in total.

  3. Finally, the chamber is turned off and the temperature decreases at a constant rate of $4$ ºC each minute until it reaches the freezing point of the sample, which is $-25$ ºC.

How long did the final cooling stage (step 3) last? What was the maximum temperature reached during the whole experiment?

Time Temp (ºC) 30 20 10 0 −10 −20 −30 −12 ºC −27 ºC −25 ºC Stage 1 −3 ºC/min × 5 ΔT = −15 ºC Stage 2 ΔT = +48 ºC Stage 3 ΔT = −46 ºC Rate: −4 ºC/min
Solve
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A delivery driver uses an elevator in a large logistics center that has floors above and below ground level (floor $0$). They take the following route: 1. Goes up from…

A delivery driver uses an elevator in a large logistics center that has floors above and below ground level (floor $0$). They take the following route:

  1. Goes up from floor $0$ to floor $+12$.

  2. Goes down $15$ floors to pick up a package.

  3. Goes up $7$ floors to deliver it.

  4. Goes down twice as many floors as they have just gone up.

  5. Finally, goes up to halfway between the floor they are on and floor $+8$.

Which floor is the delivery driver on at the end of their shift? How many floors have they traveled in total (counting both up and down)?

0 20 15 10 5 −5 −10 −15 1. Up 12 2. Down 15 3. Up 7 4. Down 14 5. Up ? End
Solve

Back to the beginning: balance, thermometer, elevator, and BC years are all solved the same way: starting value, signed moves, and operate in order.

Summary

See all the exercises in this section