This is somewhat true - economics undergrads do get into grad school, though math+econ or an econ degree with lots of math is better. You can just the check the

This is somewhat true - economics undergrads do get into grad school, though math+econ or an econ degree with lots of math is better. You can just the check the difference between the textbooks for undergrad and graduate economics, eg Principles of Economics by Mankiw (undergrad) and Mas Collel (grad).