algebra equation rather dan backsolve

[divya23]

A certain tree was first planned it was 4 feet tall then height incrsd by constt rate for next 6yrs at the end of 6th yr tree was 1/5 taller than it was at d end of 4 yr,by how many inches did the hite of tree inc each yr?
1.3/10
2.2/5
3.1/2
4.2/3
5.6/5
[spoiler]OA = 2/3[/spoiler]
[spoiler]
plz tell d correct method instead of backsolving[/spoiler]

[GMATToppers]

A certain tree was first planned it was 4 feet tall then height incrsd by constt rate for next 6yrs at the end of 6th yr tree was 1/5 taller than it was at d end of 4 yr,by how many inches did the hite of tree inc each yr?
1.3/10
2.2/5
3.1/2
4.2/3
5.6/5
The algebraic solution is as follows
4+6R=the height at the end of 6 years since 4 was already there and we added R units for 6 years
Here R is the amount of growth each year
The translation of the line "the end of 6th yr tree was 1/5 taller than it was at d end of 4 yr"
the height at the end of 6 years i have explained it above.
was means equal to '='
1/5 is 20%
taller than= add 100%
4 year height=4+4R
so
4+6R=(20%+100%)4+4R
4+6R=(120/100)4+4R
4+6R=1.2(4+4R)
R=2/3

[cans]

let constant growth rate=r
then after x years, length = 4+xt
also 4+6t = (1 + 1/5)*(4+4t)
=> 20+30t = 24+24t =>t=2/3
Thus each year growth = 2/3 inches.
IMO D

[Ozlemg]

IMO D

x is the constant growth
At the end of 1st year, its length is : 4+x
At the end of 2nd year, its length is : 4+x+x
At the end of 3rd year, its length is : 4+x+x+x
At the end of 4th year, its length is : 4+x+x+x+x
At the end of 5th year, its length is : 4+x+x+x+x+x
At the end of 6th year, its length is : 4+x+x+x+x+x+x
In the Question it is mentioned that "at the end of 6th yr tree was 1/5 taller than it was at d end of 4 yr" --> if we convert the wording to numbers, it is :

(4+4x)*(1+1/5)=4+6x
1,2x=0,8--> 2/3

[SoCan]

A certain tree was first planned it was 4 feet tall then height incrsd by constt rate for next 6yrs at the end of 6th yr tree was 1/5 taller than it was at d end of 4 yr,by how many inches did the hite of tree inc each yr?
1.3/10
2.2/5
3.1/2
4.2/3
5.6/5
[spoiler]OA = 2/3[/spoiler]
[spoiler]
plz tell d correct method instead of backsolving[/spoiler]

The question is written incorrectly - it asks for how many inches the tree grew but it gives the answers in feet. If you want the answer in feet, it's 2/3, but if you want the answer in inches, it's 8 (12 inches per foot - although the GMAT would provide this information on a real question).

[cans]

missed the growth in inches part. As no other unit was given, just assumed that all of them were same....