Question

If y=ws^3/d^4
find the % increase in 'y' when 'w' increases by 2% and 's' decreases by 3% and 'd' increasee by 1%......
There a little error in the first question i post here it is plz i need the working and explanation

Answer 1

dy/dw = s^3/d^4

dy/ds = 3 w s^2/d^4

dy/dd = [d^4(0) - 4 w s^3 d^3 ] / d^8
= - 4 w s^3 / d^5

total change:
dy = dy/dw * dw + dy/ds * ds + dy/dd * dd

if all variables are 1
y = 1
then the changes
dw = .02
ds = -.03
dd = .01
so
dy = 1 * .02 - 3 *.03 - 4 * .01
= .02 -.09 - .04
= -.11
or Down 11%

Answer 2

No calculus needed here, but Damon's exposition is clear. Let's see another easy way. The new value is

(1.02w)(0.97s)^3/(1.01d)^4
= (1.02)(0.97^3)/(1.01^4) ws^3/d^4
= 0.8946 ws^3/d^4
= 0.8946y

so, the y value has decreased by 10.54%