I=PRT I=interest P=principal=amount you invested R=rate in decimal, don't forget to convert percent to decimal T=time in YEARS (don't forget, 12 months per year)
1. I=640*0.03*2=$38.4
2. I=1500*0.0425*4=$255
3. I=580*0.02*(6/12)=$5.80
5. I=1200*0.039*(8/12)=$31.2
6. I=290*0.125*(6/12)=$18.125
7. I=75*0.125*(1/12)=0.78125, in 1 month, in interest
8. 3000, 2 years, 450=3000*2*r, 450=6000*r, divide both sides by 6000 0.075=r 7.5%=rate
9. a. 630=4200*r*3 630=12600*r divide both sides by 12600 0.05=r 5%=rate
b. 5000 total 5000-4200=800 I=800 800=4200*r*4 800=16800*r divide both sides by 16800 0.04761=r 4.761%=rate needed 6>4.7 yes