# Retail Price Index? watch

1. Ok guys, the question is:
"The UK retail price index (RPI) for the four year 1998-2001 was 160.6, 164.3, 170.3 and 171.3, where the base year was 1987 (that is, the RPI in 1987 = 100). Express the RPI for 1998 - 2001 using 1998 as the base year."
I used the formula (index = value in period t/value in base period *100) but i dont think that works if you are given the RPI and not the original price?
i'm not fishing for answers, just how do i do it?
thanks!
2. You'd want to find a number that when multiplied with the value in the new base year gives 100
then multiply that number by the given RPI for the years you're interested in.

wouldn't that do it?
3. (Original post by Joinedup)
You'd want to find a number that when multiplied with the value in the new base year gives 100
then multiply that number by the given RPI for the years you're interested in.

wouldn't that do it?
i don't have the new base number though, i only have the RPI for that year
4. i might be way off but i would:
equal 160.6 to 100 (make it the base) and then divide 160.6 by 164.3. Then divide 100 by this figure. You get 102.3 which seems respectable???
5. Oh that'd be 100 unless they specified anything different.
I'd interpret that question as asking you to re-base the RPI so that 1998=100

pretty standard for indexes of this sort to have base values of 100 or 1000 (or another nice round number)
6. (Original post by Hrov)
i might be way off but i would:
equal 160.6 to 100 (make it the base) and then divide 160.6 by 164.3. Then divide 100 by this figure. You get 102.3 which seems respectable???
yeah that's what i got in the beginning but i'm not sure. it seemed too simple.
(Original post by Joinedup)
...
yeah, i'm gonna give that a go. it's for a tutorial so ill get my answer in the end anyway

Thanks for your help guys, any more from anyone is greatly appreciated!
7. (Original post by xStaceyy)
"The UK retail price index (RPI) for the four year 1998-2001 was 160.6, 164.3, 170.3 and 171.3, where the base year was 1987 (that is, the RPI in 1987 = 100). Express the RPI for 1998 - 2001 using 1998 as the base year."
I could be off but this is what I remember, or what I would do if I had to do this question

When we're working out changes by using index numbers, essentially we are trying to calculate the percentage change from one year to the next. But we need to pick a start point, which we call 100 (because it simply makes sense that your start point is 100% of the start point lol. If it were any more/less, then it wouldn't be the start point!)

Set the index of the RPI of 1998 to 100:

Year 1998:
RPI 160.6
Index 100

What this means is that we're going to compare everything to 160.6 (the index 100 tells us we start from this point, and any other indexes are price changes relative to 160.6.)

Year 1999:
164.3
Index ?

Okay so what's the percentage of RPI in 1999 compared to 1998? Well, (164.3/160.6) * 100.
This gives you 102.3, which is your index for the year 1999. We can see that the RPI from 1998-1999 increased by 2.3%.

Hope this helped. And that it's right lol.
8. (Original post by Chelle-belle)
I could be off but this is what I remember, or what I would do if I had to do this question

When we're working out changes by using index numbers, essentially we are trying to calculate the percentage change from one year to the next. But we need to pick a start point, which we call 100 (because it simply makes sense that your start point is 100% of the start point lol. If it were any more/less, then it wouldn't be the start point!)

Set the index of the RPI of 1998 to 100:

Year 1998:
RPI 160.6
Index 100

What this means is that we're going to compare everything to 160.6 (the index 100 tells us we start from this point, and any other indexes are price changes relative to 160.6.)

Year 1999:
164.3
Index ?

Okay so what's the percentage of RPI in 1999 compared to 1998? Well, (164.3/160.6) * 100.
This gives you 102.3, which is your index for the year 1999. We can see that the RPI from 1998-1999 increased by 2.3%.

Hope this helped. And that it's right lol.
aw thank goodness im doing it correctly!
thank you so much! <3

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