Mixing the two ingredients would be adding them together:
1/2 gram + 3/4 gram = 1 1/4 total grams
Divide the total grams by 1/8 to find the number of experiments they can do:
1 1/4 / 1/8 = 5/4 / 1/8 = 5/4 * 8/1 = 40/4 = 10
They can conduct 10 experiments.