最佳解答即取10分:2條maths about percentage唔識做

Question

1) It is given that a=30 and b=50. If a and b are decrease by 5% and 8% resepectively, find the percentage decrease in their sum.

2) There are two containers of peanut oil, the normal size and the jumbo size. The volume of the normal size is less than of the jumo size by 40% and the difference in volume is 600mL.
(a) Find the volume of the normal size.
(b) If the volume of the normal size is increased by 5%, find its new volume.

Answer 1

(1) percentage change = [(new - old)/old] x100%

so we find the old sum and the new sum first,

oldSum = a+b = 30+50 = 80
newSum = a(1-5%)+b(1-8%) = 0.95a+0.92b = 0.95x30 + 0.92x50 = 74.5

% change = (74.5-80)/80 x100% = -5.5/80 x100% = -6.875%
Therefore, The percentage becrease in their sum is 6.875%


(2)
Let the volume of the jumbo size container be J and,
let the volume of the normal size container be N.

a)
J - N = 600
J - J(1-40%) = 600
J (1-1+0.4) = 600
J = 600/0.4 = 1500

So, N = J(1-40%) = 1500x(0.6) = 900
The volume of the normal size is 900mL.

b)
New volume = N(1+5%) = 900x1.05 = 945
The new volume of the normal size is 945mL.