求助一道数学题

liangzipp

When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year?

answer: 2/3

why

ddcdd

設constant amount increased each year=a

first planted=4

end of first year=4+a

end of second year=4+2a

...由此类推

end of 4th year=4+4a

end of 6th year=4+6a

当 (4+6a)= (6/5)*(4+4a)

可以算出 a=2/3