The Sexagesimal Number System
A diving team has $3$ h $15$ min of air to share among $5$ sectors of a reef. One lighthouse flashes every $18$ s and another every $45$ s: when will they flash together again? All of this can be solved with a system you already use when you read a clock: counting by $60$s.
Counting by 60s
The sexagesimal system is positional and its base is $60$: $60$ units of one order make one unit of the next order. We use it for time and for angles.
To go from complex to incomplex form, you multiply the larger unit by $60$ and add the smaller one. To go back, you divide by $60$ and the remainder is the smaller unit.
The Babylonians wrote numbers in base $60$ with two symbols: a wedge $\curlyvee$ for $1$ and another $\langle$ for $10$. Each position (each sexagesimal "digit") has a value between $0$ and $59$, and it is written by grouping tens and ones.
The sexagesimal number system is positional and has a base of $60$. State whether the following statements are true or false: a) In the sexagesimal system, $60$ units of…
The sexagesimal number system is positional and has a base of $60$. State whether the following statements are true or false:
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a) In the sexagesimal system, $60$ units of one order form one unit of the next higher order.
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b) The sexagesimal system is currently used to measure temperature.
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c) One hour has $3600$ seconds.
An architect is designing a plan and needs to work with very precise angles. If they have an angle of $45^\circ$ and $20'$, express it entirely in minutes (single-unit…
An architect is designing a plan and needs to work with very precise angles. If they have an angle of $45^\circ$ and $20'$, express it entirely in minutes (single-unit form).
The ancient Babylonians used a positional base-$60$ number system. To represent their astronomical calculations, they used symbols for $10$ ($\langle$) and for $1$…
The ancient Babylonians used a positional base-$60$ number system. To represent their astronomical calculations, they used symbols for $10$ ($\langle$) and for $1$ ($\curlyvee$). If an astronomer recorded the observation time of a star as the sexagesimal number $(12, 45, 18)$, where the first value is hours, the second minutes and the third seconds:
- a) Represent this number using Babylonian symbols (grouping the wedge marks for each position).
- b) Calculate how many total seconds the observation lasted, expressing the result in standard form.
Adding and Subtracting in Complex Form
You work column by column, just like in an addition with "carrying," but the carry happens when you reach $60$, not $10$.
In an athletics race, the first-place runner reached the finish line with a time of $1$ min $42$ s. The runner in second place arrived $15$ seconds later. What time did…
In an athletics race, the first-place runner reached the finish line with a time of $1$ min $42$ s. The runner in second place arrived $15$ seconds later. What time did the second athlete record? (Express the result in minutes and seconds).
Lucía is practicing with her telescope and has turned the lens through an angle of $120^\circ$. If she then decides to reverse the turn by $35^\circ$ $15'$, what angle…
Lucía is practicing with her telescope and has turned the lens through an angle of $120^\circ$. If she then decides to reverse the turn by $35^\circ$ $15'$, what angle does her telescope show now?
In an esports championship, the first game of a final lasted $45$ min and $38$ s. After a short break, the second game lasted $52$ min and $45$ s. Calculate the total…
In an esports championship, the first game of a final lasted $45$ min and $38$ s. After a short break, the second game lasted $52$ min and $45$ s. Calculate the total duration of both games combined and express the result in an appropriate time format.
Multiplying and Dividing by a Number
To multiply by a whole number, you multiply each unit separately and then convert whatever goes over $60$. To divide, you first share out the larger unit and convert the remainder to the next unit (multiplying by $60$) before continuing.
Why do you multiply by 60? The leftover hours can't be shared out as whole hours, but once converted to minutes they can.
A professional diving team has an air supply that allows them to stay underwater for $3$ hours and $15$ minutes. If they must divide this time equally to explore $5$…
A professional diving team has an air supply that allows them to stay underwater for $3$ hours and $15$ minutes. If they must divide this time equally to explore $5$ different sectors of a reef, how much time should they spend observing each sector?
A surveillance drone carries out a security sweep by rotating on its axis. It starts at a position of $0^\circ$ and makes the following consecutive movements: 1. Turns…
A surveillance drone carries out a security sweep by rotating on its axis. It starts at a position of $0^\circ$ and makes the following consecutive movements:
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Turns to the right through an angle of $125^\circ \ 45' \ 52''$.
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Turns to the left by $87^\circ \ 50' \ 15''$.
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Makes a third turn to the right that is exactly three times the angle resulting from subtracting the previous two movements.
Calculate the final position of the drone relative to its starting point in degrees, minutes and seconds.
In the design of a part for a high-precision engine, an angle of $145^\circ \ 25'$ must be divided into 6 equal sectors in order to place some bearings. Due to machine…
In the design of a part for a high-precision engine, an angle of $145^\circ \ 25'$ must be divided into 6 equal sectors in order to place some bearings. Due to machine limitations, the measure of each sector must be a whole number of minutes (no seconds) and as large as possible. When carrying out the division, the leftover angle is shared equally between two lateral safety margins.
The drawing is not to scale: the margins are so small that they cannot be seen.
- a) Calculate the measure of each of the 6 sectors.
- b) Calculate the leftover angle and the measure of the angle of each safety margin.
Decimals, Hundredths, and Complex Form
Sometimes you have a decimal and want it in complex form. You separate the whole part from the decimal part and multiply the decimal part by $60$; if another decimal part is left, you multiply by $60$ again.
If you want a fraction of a turn (a decimal of an orbit), you multiply by the $360^\circ$ in a full turn and then convert the decimal part of the degrees to minutes. To find out how long one lap takes, you divide the total time by the number of laps: the quotient in hours is converted to minutes and the minutes to seconds, as in the previous section.
In timekeeping, hundredths of a second are also used: $1\text{ s} = 100$ hundredths. Hundredths are added separately, like decimals, and if they go over $100$ you carry $1$ second.
A telecommunications satellite orbits the Earth. On their control panel, a technician observes that the satellite has completed $4.72$ orbits in the last $24$ hours. a)…
A telecommunications satellite orbits the Earth. On their control panel, a technician observes that the satellite has completed $4.72$ orbits in the last $24$ hours.
- a) Express the decimal part of the orbits ($0.72$) in compound unit form using degrees, minutes and seconds (knowing that a complete orbit is $360^\circ$).
- b) If the satellite takes the same time for each orbit, what is the exact time it takes to complete a single turn? Express the result in hours, minutes and seconds.
A video editor is working on a short film for social media. The project has a strict time limit of exactly $10$ minutes. They have four clips with the following…
A video editor is working on a short film for social media. The project has a strict time limit of exactly $10$ minutes. They have four clips with the following durations:
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Clip 1: $2$ min $14$ s $45$ hundredths.
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Clip 2: $155$ s $80$ hundredths.
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Clip 3: $3$ min $12$ s.
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Clip 4: $1$ min $58$ s $95$ hundredths.
Calculate the exact time left over or needed to reach the limit of $10$ minutes. (Remember that $1$ second has $100$ hundredths).
Periodic Coincidences
If two signals repeat every $a$ and every $b$ seconds, they coincide every $\text{LCM}(a, b)$ seconds. With three signals, you calculate the LCM of the three periods.
Why the LCM? To coincide, the elapsed time must be a multiple of both periods. The first time that happens is at the least common multiple.
A lighthouse emits three different light signals to guide ships: The red light flashes every $18$ seconds. The green light flashes every $45$ seconds. The white light…
A lighthouse emits three different light signals to guide ships:
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The red light flashes every $18$ seconds.
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The green light flashes every $45$ seconds.
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The white light flashes every $1$ minute and $15$ seconds.
If at $22:00:00$ at night all three lights flash together for the first time:
- a) How much time will pass until they flash together again? Express the result in minutes and seconds.
- b) At what exact time will they flash together for the second time?
- c) How many times will all three lights flash together from $22:00:00$ to $00:00:00$, both times included?
Angles of a Polygon
The sum of the interior angles of a polygon with $n$ sides is $S = (n - 2) \times 180^\circ$. If you know all of them except one, you get it by subtracting in complex form. The reason for the formula is that a polygon with $n$ sides can be divided into $n - 2$ triangles, and each triangle adds up to $180^\circ$.
To add five angles, add them column by column: first seconds (if they go over $60$, you carry minutes), then minutes (if they go over $60$, you carry degrees), and finally the degrees.
The complementary angle of a given angle is what it lacks to reach $90^\circ$. It is calculated as $90^\circ$ minus the angle, "borrowing" just as before.
In a technical drawing class, we are asked to draw the complementary angle of a given angle. If the original angle measures $34^\circ 52' 18''$, carry out the necessary…
In a technical drawing class, we are asked to draw the complementary angle of a given angle. If the original angle measures $34^\circ 52' 18''$, carry out the necessary calculations to find the exact measure of the angle needed to complete the right angle ($90^\circ$).
In an irregular hexagon, the measurements of five of its interior angles are known: $A = 110^\circ \ 15' \ 20''$ $B = 125^\circ \ 40'$ $C = 98^\circ \ 25''$…
In an irregular hexagon, the measurements of five of its interior angles are known:
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$A = 110^\circ \ 15' \ 20''$
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$B = 125^\circ \ 40'$
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$C = 98^\circ \ 25''$
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$D = 130^\circ \ 12' \ 15''$
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$E = 115^\circ \ 50' \ 30''$
Given that the sum of the interior angles of a $n$-sided polygon is $S = (n - 2) \times 180^\circ$, calculate the measure of the sixth angle $F$ in compound form.
Summary
Back to the beginning: the divers have $39$ min per sector, and the lighthouses with periods of $18$ s and $45$ s coincide every $90$ s.