Higher June 2018 Paper 3 Q10
10 Here are three lamps.
Lamp A flashes every 20 seconds.
Lamp B flashes every 45 seconds.
Lamp C flashes every 120 seconds.
The three lamps start flashing at the same time.
How many times in one hour will the three lamps flash at the same time? (3)
| Answer | Mark | Mark scheme |
|---|---|---|
| 10 | P1 | for start to a process to find the LCM of 20, 45 and 120 (= 360), eg \(45 = 3 \times 3 \times 5\) or \(20 = 2 \times 2 \times 5\) or \(120 = 2 \times 2 \times 2 \times 3 \times 5\) or writes down at least 3 multiples of 45 and 120 |
| P1 | (dep) for a process to find number of times/hour using their LCM, eg \(3600 \div 360\) or \(3600 \div 720\) | |
| A1 | for 10 or 11 |
Additional guidance
Could be presented as complete prime factor trees for 45 or 120
Must use a common multiple.
Working may be in minutes.