Math : I have no idea how to approach this question? few can do this

In an experiment, 6 bulbs were planted in a row. 3 produced red flowers, and 3 produce yellow flowers.

If the bulbs were planted in random order, if the bulbs were planted in random order what is the probability the colours will occur alternately?

no calculator allowed, to be done in under two minutes

i genuingly can not do this

i thought

3/6 = red
3/6 = yellow

1/2 ^ 2

but apprently it's 1/10

It would have to be either RYRYRY or YRYRYR.
Each has probability 3/6 • 3/5 • 2/4 • 2/3 • 1/2 • 1 = 36/720 = 1/20

so 1/20 + 1/20 = 2/20 or 1/10