Ratio P6 A001

At first, Serene had 1/5 as much money as Kelly. Then Mrs Chan gave Serene $20 and gave Kelly $12, the ratio of Serene's sum of money to Kelly's sum of money became 1 : 4. How much money had Kelly in the end?

S [      ][20]

K [      ][      ][      ][      ][      ][     12    ]

   [      ][20][      ][20][      ][20][      ][20]

Compare K.

5 u + 12 --> 4 u + 4 x 20

1 u -- > 80 – 12 = 68

5 u -- > 5 x 68 = 340

340 + 12 = 352 cookies

Kelly had 352 cookies in the end.

Alternative method 1

            S         K

     x 4 ----------------   Multiply column S by 4 to get the

     4       1    :    5      end stage the same (4) as K.
+ 80  + 20     + 12
-------------------------
     4       1     :   4
-------------------------

5 u + 12 --> 4 u + 4 x 20

1 u -- > 80 – 12 = 68

5 u -- > 5 x 68 = 340

340 + 12 = 352 cookies

Kelly had 352 cookies in the end.

Alternative method 2

            S         K

     x 5 ----------------  Multiply column S by 5 to get the
     5       1    :    5     beginning stage the same (5) as K.
+ 100 + 20     + 12
-------------------------
     5       1     :   4
-------------------------

5 u - 100 --> 4 u - 12

1 u -- > 100 – 12 = 88

4 u -- > 4 x 88 = 352 cookies

Kelly had 352 cookies in the end.