This blog post from Solve My Maths is a treasure trove of deep thinking fractions questions.
This image inspired me to plan a group activity with a class.
Give each group a set of coloured stickers (8 different colours – getting ones that exactly match the picture could be a challenge! I might need to make my own and then take a photo. Maybe a grid in the background would be helpful if I do this…)
Show the left-most and the right-most column of numbers on this image and hide the stickers in the middle. Their challenge is to fill in the ones in the middle. They can use calculators if they like – seeing a fraction as the equivalent of the operation of dividing numerator by denominator is useful. Work together, only place the sticker if everyone else in your group agrees. I think this will really get them talking.