For the first week, her investment gain is $400 * 25% = $<<400*25*.01=100>>100.
This leaves her investment with a value of $400 + $100 = $<<400+100=500>>500.
For the second week, her investment increased by $500 * 50% = $<<500*50*.01=250>>250.
Pima's investment in Ethereum is now worth a total of $500 + $250 = $<<500+250=750>>750.
#### 750