A student wants to know if girls are better at balancing than boys. She gathers 25 of her 12 year old female friends and 25 boys who are also 12 years old. Her hypothesis is that girls will have better balance. She sets up a balance beam 1 foot off the ground and has each student walk across 2 times. She counts how many times they slip off the beam and records her data in a chart. At the end of her experiment, she has noticed that the girls fell off the beam a total of 10 times and the boys fell off 15 times all together. Did she use a “control group”?

Ascientist is investigating the effects of salinity on fish development. he places fertilized fish eggs in an aquarium that contains low salinity and observes their development. what factor would improve experimental design the most? place the fish eggs in the open ocean because that is the natural habitat include another aquarium that has normal salinity to compare to the low salinity aquarium include an aquarium that replaces salt with sugar to confirm that the effects are specific to salt grow algae with the fish eggs in order to provide adequate nutrients to the developing embryos