<ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1:2 .  On the o...
<ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2.  On the ...
<ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2.  On the ...
<ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2.  On the ...
<ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2.  On the ...
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Case 1 - Case 2

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Case 1 - Case 2

  1. 1. <ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1:2 . On the other hand, when 10 girls leave the classroom, there are as many girls as boys. How many pupils are there in the class? </li></ul>C1 – C2 Total Unchanged
  2. 2. <ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2. On the other hand, when 10 girls leave the classroom, there are as many girls as boys. How many pupils are there in the class? </li></ul>Step 1 Case 1 C1 – C2 Total Unchanged Girls Boys Before Change After ? ? – 10 2u 1u
  3. 3. <ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2. On the other hand, when 10 girls leave the classroom, there are as many girls as boys. How many pupils are there in the class? </li></ul>Step 1 Case 1 Case 2 Step 2 C1 – C2 Total Unchanged 2u ? Girls Boys Before ? Change – 10 After 1u 3p Girls Boys Before Change After 5p ? ? – 10 4p 5p
  4. 4. <ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2. On the other hand, when 10 girls leave the classroom, there are as many girls as boys. How many pupils are there in the class? </li></ul>Step 1 Case 1 Case 2 Step 2 Step 3 Note: Since we minus 10 from the before-total in both cases, the after-total in both cases is unchanged C1 – C2 Total Unchanged 2u Girls Boys Before Change – 10 After 1u x4 =4p 4p – 10 Girls Boys Before Change After 5p 3u Total 9p Total x3 =9p 2u x3 =6p 1u x3 =3p 6p 3p+10 4p+10 5p
  5. 5. <ul><li>In a classroom, when 10 boys leave the classroom, the ratio of the remaining boys to girls becomes 1 : 2. On the other hand, when 10 girls leave the classroom, there are as many girls as boys. How many pupils are there in the class? </li></ul>Step 1 Case 1 Case 2 Step 2 Step 3 Step 4 5p  3p + 10 2p  10 1p  10 ÷ 2 =5 5p  5 x 5 = 25 (B) 6p  6 x 5 = 30 (G) 30 + 25 = 55 Ans: 55 pupils C1 – C2 Total Unchanged 2u x3 =6p 6p Girls 3u x3 =9p Total Boys Before 3p+10 Change – 10 After 1u x3 =3p 4p – 10 4p+10 Girls 9p Total Boys Before 5p Change After 5p

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