Page 291 - ICSE Math 8

Formula Sheet

PERCENTAGE

‘Per cent’ means ‘for every 100’
Operation Method Example(s)

Converting a Multiply by 100 and put the % 6 6
fraction or a symbol (a) 15 = 15 × 100% = 40%
decimal to %-age (b) 0.36 = 0.36 × 100% = 36%
64.5 129
Converting a %-age Remove the % symbol and (a) 64.5% = =
to a fraction or a divide by 100 100 200
decimal (b) 37% = 37 = 0.37
100

To express X as a X  24 
%-age of Y Y × 100% ` 24 as %-age of `192 =   192   × 100% = 12.5%

To find the given  %-age × X 15% of ` 7,500=  15  × ` 7,500 = ` 1,125
%-age of X   100     100  

To find X from the Given %-age of X ÷  %-age  26% of a number is 41.6. Find the number.
26 

given %-age of X   100   41.6 ÷   100   = 160
 Increase in value X decreased by 17% is 531.2.
  × 100 %
Increase or  Original value  X –  17X  = 531.2 or,
Decrease %-age  Dercrease in Value   100  
  × 100 %
 Original value  X = 640

VOLUME AND SURFACE AREA OF SOLIDS

Name of Solid Surface Area Volume Remarks
Cuboid 2(l × b + b × h + l × h) l × b × h l = Length,
Diagonal 2 l + 2 b + 2 h 2 b = Breadth, h = height
LSA 2h(l + b) LAS = Lateral Surface Area
Cube a × a × a or, a 3 a = side of cube
SA 6a 2 SA = Surface Area
Diagonal 3a
LSA 4a 2
2
Rt. Circular pr h r = radius of cylinder,
Cylinder h = height of cylinder,
LSA 2prh R = external radius of cylinder
TSA 2pr(h + r) TSA = Total Surface Area
CSA(hollow) 2ph(R + r) ph(R – r ) CSA = Curved Surface Area
2
2
TSA(hollow) {2p(R + r)(h + R – r)}

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