# Maths Unit C

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• Created by: kirsty
• Created on: 11-06-13 11:52
• Maths Unit C
• Direct and inverse proportion
• Inverse
• y   1/x read as 'y is inversely proportional to x'
• example y=5 when x=4 5=m/4  5x4=m=20 y=20/x
• further examples: find y when x=30 y=20/30=0.6 find x when y=25  25=20/x x=20/25=0.8
• Direct
• y   x   read as 'y is directly proportional to x'
• example: y=1.8 x=9 y=mx 1.8=mx9 1.8/9=m=0.2 y=0.2x
• further examples: find y when x=52 y=0.2x52 =10.4          find x when y=42   42=0.2 * x 42/0.2=x=210
• percentage increase and decreases
• Increase
• 100%+ (the percentage increase) then that number x by original amount
• Example: Julie is given a pay rise of 3.5% on her current salary of 34900 so: 100%+3.5%= 103.5% 34900x103.5 = 36121.50
• Decrease
• 100%-(the percentage decrease) then this number x by original amount
• example: work out the new price of a camera that did cost £480 before the 22% reduction so: 100%-22%= 78% 480x0.78=£374.40
• circles
• circumferene  = pie x diameter
• example=  pie x 8 = 8pie= 25.13274123
• area = pie x r squared
• example pie x 4 squared = 16 pie = 50.26548246
• for sectors for both area and circumference you just do the angle of the sector divided by 360 and then the same as you did for the others.
• cherry pies delicious! apple pies are too!
• Factorising
• examples: PQR+RST = R(PQ+ST) 4XY-8X = 4(XY-2X) 2A+2B = 2(A+2B)
• factorising a x"+4x+3=0 you would get (x+3) and (x+1) this is because the numbers add to make the middle and times to make the end number.
• expanding:  4(5a+2) = 20a +8   3x(2-9y) = 6x-9xy 3(2x+5) = 6x+15
• when cant factorise use the quadratic formula!
• y   1/x read as 'y is inversely proportional to x'
• example y=5 when x=4 5=m/4  5x4=m=20 y=20/x
• further examples: find y when x=30 y=20/30=0.6 find x when y=25  25=20/x x=20/25=0.8
• for surface areas you add the area of each surface altogether,