FREQUENTLY MADE MISTAKES TOPIC LENGTH, MASS AND VOLUME OF LIQUID

LENGTH

1.   Mistakes when subtracting , adding, multilying or dividing involving conversion of units.

Example  :

a)   76.8 m  -  51 cm  =  25.8  m  (wrong because cm was not converted to m )
       76.8 m  -  51 cm  =  76.29 m  (correct )

b)  432 m  x  16   =  6 912 km    ( wrong to change the unit without converting the value )
      432 m  x  16  =  6.912  km    (correct)


MASS

1.   Mistakes in calculation involving different units.

Example  :
 
 a)   6.87  kg  =    (6.87 x 100)      =  687  g        (wrong because 1 kg is not equal to 100 g)
        6.87  kg  =   (6.87 x 1 000 )  =  6 870 g      ( correct because 1 kg is equal to 1 000 g )


2.   Mistakes when multiplying

Example  :

a)   15 kg  781  g  X  6  =  90 kg  4 686 g  ( wrong because 4 686 g is not converted to kg)
       15 kg  781 g  X  6  =  94 kg  686  g    ( correct because 4000  g is converted to 4 kg)


VOLUME OF LIQUID

1.   Did not arrange decimal points in a vertical line.

Example  :

a)  9.8  L  +  17.4 L  +  239.76  L  =  1 317.476  L  ( wrong because the decimal point are not arranged)
     9.80  L  +  17.40 L  +  239.76  L  =  266 . 96 L  (correct because decimal point arranged in vertical line)


2.   Mistakes when performing operations involving conversions of units.

Example  :

a)  280 ml  +  13  l  +  1 540 ml  =  1 833 l  (wrong because did not change ml to l )
     0.28 l  +  13.00 l  +  1.54 l     =  14.82  l  (correct because change ml to l )



   



   

FREQUENTLY MADE MISTAKES TOPIC PERCENTAGE, MONEY, TIME

PERCENTAGE

1.  Mistakes made when converting fractions to percentages.

Example  :  3/5  =  ______  %

3/5  =  _____ %                             3/5  =  ____ %
3/5  =  (  3/5 )  %                            3/5  =  (3 x 20) / (5 x 20)  =  60 / 100
       =   0.6  %         (wrong)                  =  60 %       (correct)


2.  Mistakes made when converting percentages to decimals

Example  :   Convert 275 %  to a decimals.

275 %  =  275/100  x  100                           275 %  =  275/100
             =  275           (wrong)                                  =  2.75          (correct)


3.   Mistakes in counting percentages

Example   :  5 %  of 200

5 %  of  200    =   5 x  200                         5 %  of  200   =  5/100  x  200
                        =  1 000   (wrong)                                    =  10    (correct)


MONEY

1.   Mistakes made when adding and subtracting money, decimal point must be arranged in a straight line.

Example  :   RM 567.20 + RM 12 + RM 4 208  =


2.   Mistakes made when performing operations involving brackets. Calculation must be done in brackets first.

Example  :  RM  7 325.55  x  ( 5 + 4 )  =



TIME

1.   Mistakes in the units of measurements of time.

Example  :  5 hr 42 min  +  3 hr 50 min  =

5 hr 42 min  +  3 hr 50 min  =  8 hr 92 min       ( wrong )   because 92 min is more than 1 hour
5 hr 42 min  +  3 hr 50 min  =  9 hr 32 min       (correct )


2.   Mistakes in calculating the numbers of days between two given dates.

Example  :  Calculate the number of days between 19 Sept 2008  and  28 Sept 2008

Number of days from 19-28 Sept. 2008                        
=  ( 28 - 19 ) days
=  9 days                   (wrong)

Number of days from 19-28 Sept. 2008
= ( 28 - 19 + 1 ) days
=  10 days                (correct)
( 19 Sept. 2008 is count as 1 day )