Question

one light flashes every 4 seconds. another light flashes every 10 seconds. if both lights flash at the same time now, how many seconds will it take for them to flash together again?

Explanation:

Step1: Find prime factors of 4

$4 = 2^2$

Step2: Find prime factors of 10

$10 = 2 \times 5$

Step3: Calculate LCM of 4 and 10

$\text{LCM}(4,10) = 2^2 \times 5 = 20$

Answer:

20