Hello!
First you have to put the horses weight into grams
There are 1000 kilograms in a gram
Multiply the horse weight by 1000 to get its weight in grams
500 * 1000 = 500000g
Divide the weight of the horse by the weight of the spider
500000 / 1 = 500000
The answer is 500,000 spiders
Hope this helps!