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# Maths 1 sat 2 Help!

Registered User Posts: 4 New Member
Hey guys!
So i finished a practice test for maths 1 from holt college.However they were a few questions which I could not understand.If anyone could help,that would be great! Its from http://репетиторвкиеве.рф/wp-content/uploads/2015/05/SAT-math-IC-no-answers.pdf and it is questions 20,30,31,34
Thanks

## Replies to: Maths 1 sat 2 Help!

• Registered User Posts: 904 Member
20) Substitute x=a+b into the original expression and then simplify using the exponent rules.
2^(a+b)+(2^a)(2^b)=2^(a+b)+2^(a+b)=2(2^(a+b))=2^(a+b+1)

If you don't know the exponent rules, you can solve with a CAS calculator, Just subtract each answer choice from
2^(a+b)+(2^a)(2^b). The choice that gives a difference of 0 is the correct answer.
• Registered User Posts: 904 Member
30) Probability= (Volume of Sphere)/(Volume of Cube)
Side of cube= 2r
Volume of sphere= (4/3) (pi)r^3
Volume of cube=(2r)^3=8r^3
ratio4(pi)/3/(8)= pi/6

• Registered User Posts: 904 Member
31, CAS Calc solution
solve(sqrt(a*x-1)-sqrt(a*x+1)=sqrt(ax),x) Enter
returns x= 2sqrt(3)/3a
• Registered User Posts: 4 New Member
Thank you so much @Plotinus !!
• Registered User Posts: 4 New Member
Would plugging in also work for question 20? i.e. x=3 a=2 and b=1 so from the equation in the question its equal to 16? and just look for the same answer in one of the choices?
Also is cas allowed in a sat exam?
• Registered User Posts: 904 Member
@kayaale

Plugging in numbers would work fine for question 20. There are multiple ways to do these questions. You should use the method that works best for YOU.

CAS is most definitely allowed for all SAT math exams except the non-calculator part of the redesigned SAT regular test. However, if you plan to get a CAS calculator, make sure you spend plenty of time practicing with it before test day. On test day, use the calculator only for operations you have already practiced and know how to do well.
• Registered User Posts: 4 New Member
@Plotinus would you recommend a cas function calculator for maths 1? I have my test on the first so don't really know if i should invest in it? Once again,thank you so much!
• Registered User Posts: 904 Member
I would not recommend getting a new calculator now for a test on October 1. You would have less than 1 week to learn to use it, and this is not enough unless you are great with calculators.
This discussion has been closed.