adding &subtracting fractions

What number could be a common denominator for these two fractions?
2/3   and   3/4

• 3
• 4
• 7
• 12

What is the sum of these fractions?

• 4/5
• 3/20
• 17/20
• 4/20

If you color in 2 more slices what is the fraction?

• 3/8
• 6/8
• 5/8
• 5/9

A plumber is fitting a water pipe that is 3/4 foot long on to a water pipe that is 2/12 foot long. How long will the finished pipe be?

• 11/12 foot
• 8/16 foot
• 2/12 foot
• 1 foot

1/4 + 2/5 =

• 2/20 
• 1/2
• 13/20
• 2/16

1 3/4 - 2/3 =

• 1 1/12
• 1 2/6
• 21/12
• 8/12

8/15 + 2/3=

• 4/10
• 6/5
• 1/15
• frog girl

1/12 + 3/10=

• 23/60
• 24/60
• 21/60
• 3/4

5/8 - 2/5=

• 9/40
• 8/40
• 7/35
• frog boy

What will be the common denominator? 
2/5 - 3/10 =

• 8
• 5
• 12
• 10