Determining original investment for simple interest with two unknowns

Joined
Dec 2, 2018
Messages
1
Okay heres the question word for word;

**A bank offers a choice of two fixed term deposits.

Option A: Earning simple interest at 6.5 % p.a. for 4 years.

Option B: Earning simple interest at 8% p.a. for 3.5 years

David invests the same amount of money in both option A and B. Option B earns $105 more than option A.

Determine David's original investment.**
Okay so here's my working so far;

I=Prt
I=(P)(0.065)(4) & I=(P)(0.08)(3.5)

Therefor;

((P)(0.08)(3.5))-((P)(0.065)(4)) = 105

But then I get stuck because I can't figure out how to find the simple interest without knowing P.

I know the formula for principal is

P= I/(rt)

But I cant find that without knowing the simple interest. I feel like the answer is right in front of me but yeah I'm very confused.The answer is meant to equal $5250 in the book but no matter what I do I can't seem to get it to equal that.
 
Okay heres the question word for word;

**A bank offers a choice of two fixed term deposits.

Option A: Earning simple interest at 6.5 % p.a. for 4 years.

Option B: Earning simple interest at 8% p.a. for 3.5 years

David invests the same amount of money in both option A and B. Option B earns $105 more than option A.

Determine David's original investment.**
Okay so here's my working so far;

I=Prt
I=(P)(0.065)(4) & I=(P)(0.08)(3.5)

Therefor;

((P)(0.08)(3.5))-((P)(0.065)(4)) = 105

But then I get stuck because I can't figure out how to find the simple interest without knowing P.

I know the formula for principal is

P= I/(rt)

But I cant find that without knowing the simple interest. I feel like the answer is right in front of me but yeah I'm very confused.The answer is meant to equal $5250 in the book but no matter what I do I can't seem to get it to equal that.

You're right: it is right in front of you.

You wrote the equation ((P)(0.08)(3.5))-((P)(0.065)(4)) = 105. Solve it for P!
 
Top