Can someone check these answers for me? (1 Viewer)

[ptrgrgry]

These are easy questions, but I can't get the same answer as the textbook (either I'm retarded or the textbook is):

1. In 1976, 500 students entere for a particular examination. This number increased each year by 20% of the number who had entered in the previous year. Calculate the number who entered in 1981.

2. The value of a motor car when new is $8000. Its value depreciates each year by 15% of its value at the beginning of that year. After how many years will its value be $4000. (Answer is written as between a and b years).

 

[mirakon]

The first one should have the answer 500(1.2)^5 whatever that is= 1244 i think

for second one

4000=8000(0.85)^n

0.5=0.85^n

Take ln of both sides

ln(0.5)=n x ln(0.85) By log laws index comes down, remember

Therefore

n= ln0.5/ln0.85 then approximate this appropriately to get the year

 

[ptrgrgry]

That's what i got
textbook says:
Q.1) is 1245
- I wrote 1244
Q.2) between 4 to 5 years
- I think it should be between 5 and 6 years.

 

[hscishard]

4-5 is correct, as there is no power to the (n-1)

The first one I think should be 1245, as there can't be .16 of a student.

 

[ptrgrgry]

4-5 is correct, as there is no power to the (n-1)

Oh, right you are.
Thanks

 

[mirakon]

Actually it is 1245 as 1244.16 rounds up as hscishard is correct, you can't have a fraction of a student.

 

[ptrgrgry]

How does .16 round up?

 

[thongetsu]

always round up!

 

[annabackwards]

always round up!

Yes, when it has to do with quanities involving things like humans, cars which you cannot have a fraction of XD

When rounding normal values, don't just round up lol.

 

[bouncing]

always round up!

i thought it was rounding down?? :\

if we have 199.6 people dont we actually only have 199 people?

 

[slyhunter]

i thought it was rounding down?? :\

if we have 199.6 people dont we actually only have 199 people?

What happens to the 0.6 of a person? We assume the 0.6 is one person, hence the rounding up.

 

[annabackwards]

What happens to the 0.6 of a person? We assume the 0.6 is one person, hence the rounding up.

*nods*

It's like ordering/making food for a party. You always make it for more people than are expected to come ^^

 

[bouncing]

*nods*

It's like ordering/making food for a party. You always make it for more people than are expected to come ^^

oh right.. now i feel stupid >< dah