Question

How many eighth-size parts do you need to model 3/4? explain

Answer 1

To know the amount of eights you want to get something that looks like ?/8. Basically, the bottom number needs multiplying by 2 (8 divided by 4 is 2). To keep the fraction accurate you multiply by 2 the top and bottom number so you get: 
3/4=(3x2)/(4x2)=6/8