least common multiple of 20, 15, and 35
Here are the multiples of 35 that end in 0.
70, 140, 210, 280, 350, 420, 490
Are any of them divisible by both 20 and 15?
If not, keep going.
70, 140, 210, 280, 350, 420, 490
Are any of them divisible by both 20 and 15?
If not, keep going.