Page 168 - NUMINO Challenge_D1
P. 168
Problem solving Problem solving
1 Since the minute hand moves 6 per minute, it 1 The distance between two consecutive notches
will take 210 6 35 minutes to move 210 . on the clock forms an angle of 15 . The hour
The hour hand moves 0.5 per minute, so it will hand moves 15 60 0.25 per minute, and
move 0.5 35 17.5 in 35 minutes. The time the minute hand moves 360 60 6 per
then will be 5:10 35 minutes 5 : 45. minute. If the hour hand points to 14 and the
minute hand points to 6, the angle formed by
2 From 1 o'clock until the time the crime the hands is 15 8 120 . Since the hour hand
moves 0.25 15 3.75 in 15 minutes, the
happened, the minute hand moved 150 more angle is 120 3.75 123.75 .
than the hour hand. Since the minute hand
moves 5.5 more per minute than the hour
3
hand, it took 150 5.5 27 11 minutes. 2 The hour and minute hand overlap 8 times in 9
3 hours (405 min). The time that they overlap for
11
Therefore, the crime happened at 1 : 27 . the first time after 9 o'clock is
405 min. 8h 50 5 min. 1 : 5 5 .
8 8
Type 15-2 A Special Clock p.132~p.133
Creative Thinking p.134~p.135
1 The hour hand moves 360 in 9 hours, so the 1 At 5 o'clock, the minute hand is 150 behind the
angle between each number is 360 9 40 .
Therefore, the angle between number 8 and 1 is hour hand. Since the movie lasted for more than
40 2 80 .
10 minutes, the minute hand was 110 in front
2 The hour hand makes 1 complete revolution in 9 of the hour hand at the time the movie ended.
hours, which means that it rotates 360 9 40
Therefore, the minute hand moved 150
per hour. 110 260 more than the hour hand during the
Therefore, it will move 40 5 4 4 in 5 minutes. movie. The minute hand moved 5.5 more per
45 9 3
minute, so the movie lasted 260 5.5 47 11
minutes.
3 80 4 4 75 5 The movie ended at 5 : 47 3 .
9 9 11
2 The elapsed time between two consecutive
5
times the hands overlap is 720 11 65 11
minutes. During studying, the clock hands will
overlap 3 times.
65 5 3 196 4 3 hours and 16 4 minutes
11 11 11
Answer Key
1 Since the minute hand moves 6 per minute, it 1 The distance between two consecutive notches
will take 210 6 35 minutes to move 210 . on the clock forms an angle of 15 . The hour
The hour hand moves 0.5 per minute, so it will hand moves 15 60 0.25 per minute, and
move 0.5 35 17.5 in 35 minutes. The time the minute hand moves 360 60 6 per
then will be 5:10 35 minutes 5 : 45. minute. If the hour hand points to 14 and the
minute hand points to 6, the angle formed by
2 From 1 o'clock until the time the crime the hands is 15 8 120 . Since the hour hand
moves 0.25 15 3.75 in 15 minutes, the
happened, the minute hand moved 150 more angle is 120 3.75 123.75 .
than the hour hand. Since the minute hand
moves 5.5 more per minute than the hour
3
hand, it took 150 5.5 27 11 minutes. 2 The hour and minute hand overlap 8 times in 9
3 hours (405 min). The time that they overlap for
11
Therefore, the crime happened at 1 : 27 . the first time after 9 o'clock is
405 min. 8h 50 5 min. 1 : 5 5 .
8 8
Type 15-2 A Special Clock p.132~p.133
Creative Thinking p.134~p.135
1 The hour hand moves 360 in 9 hours, so the 1 At 5 o'clock, the minute hand is 150 behind the
angle between each number is 360 9 40 .
Therefore, the angle between number 8 and 1 is hour hand. Since the movie lasted for more than
40 2 80 .
10 minutes, the minute hand was 110 in front
2 The hour hand makes 1 complete revolution in 9 of the hour hand at the time the movie ended.
hours, which means that it rotates 360 9 40
Therefore, the minute hand moved 150
per hour. 110 260 more than the hour hand during the
Therefore, it will move 40 5 4 4 in 5 minutes. movie. The minute hand moved 5.5 more per
45 9 3
minute, so the movie lasted 260 5.5 47 11
minutes.
3 80 4 4 75 5 The movie ended at 5 : 47 3 .
9 9 11
2 The elapsed time between two consecutive
5
times the hands overlap is 720 11 65 11
minutes. During studying, the clock hands will
overlap 3 times.
65 5 3 196 4 3 hours and 16 4 minutes
11 11 11
Answer Key
