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ESO Y2 · Mathematics
Numbers · Other number systems

The sexagesimal numeration system

A diving team has $3$ h $15$ min of air to share between $5$ sections of a reef. One lighthouse flashes every $18$ s, another every $45$ s: when will they next flash together? You already know the sexagesimal system (counting in $60$s) for adding and subtracting times and angles; now it is time for multiplication, division and the problems that combine them.

Review: counting in 60s

Diagram of sexagesimal equivalences: one hour equals sixty minutes, one minute equals sixty seconds, one degree equals sixty minutes and one minute of angle equals sixty seconds. Hours 1 h = 60 min 1 min = 60 s Degrees 1° = 60' 1' = 60''
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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?

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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.

Solve

Multiplying and dividing a time or an angle by a number

To multiply a sexagesimal measurement by a whole number, you multiply each unit separately and then convert whatever goes over $60$. To divide, you share out starting with the largest unit and "carry down" the remainder to the next unit, just like a division of whole numbers.

Outline of the procedure for dividing a sexagesimal measurement by a whole number, passing the remainders on to the next unit. 3 h 15 min : 5 3 h : 5 = 0 h, remainder 3 h = 180 min 180 min + 15 min = 195 min 195 min : 5 = 39 min per section
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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?

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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 ($90^\circ$).

34° 52' 18'' ? 90°
Solve

Periodic coincidences: the LCM in seconds

If several signals repeat every certain number of seconds, working out when they all coincide is a problem about common multiples.

Animation of two timelines: a cursor moves from 0 to 90 seconds, lighthouses A (every 18 s) and B (every 45 s) flash as the cursor passes their marks, and at 90 s they flash together, highlighting the coincidence in green. lighthouse A: every 18 s lighthouse B: every 45 s 0 18 36 54 72 90 0 45 90 they coincide again: LCM(18, 45) = 90 s
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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:

  • The red light flashes every $18$ seconds.

  • The green light flashes every $45$ seconds.

  • 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:

  1. a) How much time will pass until they flash together again? Express the result in minutes and seconds.
  2. b) At what exact time will they flash together for the second time?
  3. c) How many times will all three lights flash together from $22:00:00$ to $00:00:00$, both times included?
Solve
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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:

  • Clip 1: $2$ min $14$ s $45$ hundredths.

  • Clip 2: $155$ s $80$ hundredths.

  • Clip 3: $3$ min $12$ s.

  • 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).

Solve

Angles in polygons and more than two terms

The sum of the interior angles of a polygon with $n$ sides is $S = (n-2) \cdot 180°$. If you know all the angles except one, you can find it by subtracting in compound form.

Irregular hexagon with the formula for the sum of its interior angles and the calculation of the unknown angle by subtraction. sum of the 6 angles = (6-2)·180° = 720° F = 720° − (A+B+C+D+E)
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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:

  • $A = 110^\circ \ 15' \ 20''$

  • $B = 125^\circ \ 40'$

  • $C = 98^\circ \ 25''$

  • $D = 130^\circ \ 12' \ 15''$

  • $E = 115^\circ \ 50' \ 30''$

Given that the sum of the interior angles of a $n$-sided polygon is $S = (n - 2) \cdot 180^\circ$, calculate the measure of the sixth angle $F$ in compound form.

A B C D E F = ? S = (6-2)·180° = 720°
Solve
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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:

  1. Turns to the right through an angle of $125^\circ \ 45' \ 52''$.

  2. Turns to the left by $87^\circ \ 50' \ 15''$.

  3. 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.

Solve

Summary

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