Rachel and Sean had the same number off marbles. Rachel gave away 20 marbles and Sean gave away 44 marbles. Rachel then had 3 times as much as Sean. How many ma

Question

pls give it in basic singapore math pls not algebra so that i may understand it :) Thanks

Answer 1

 

No algebra, so we must do it numerically

Set up a table

 

# of marbles      Rachel gave away 20      Sean gave away 44

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  50                                 30                          6               <----  not 3 times as big, guess again

  100                               70                         56               <----   not 3 times as big, try again, guess smaller

  75                                 55                         31               <--- closer, guess again

  60                                 40                         16               <--- closer, guess again

  55                                 35                         11

  57                                 37                         13              <---- closest so far

  56                                 36                         12             <---- FOUND THE ANSWER

 

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For those interested in the algebra , read on:

 

 ? is the number of marbles they each have.

 

 ? - 20 = 3 x (? - 44)

 

? - 20 = 3 x ? - 3 x 44  <--- distributive property

 

? - 20 = 3 x ? - 132

 

0 = 3 x ? - 132 - ? + 20

 

0 = 2 x ? - 112  <--- combines like terms

 

112 = 2 x ?

 

? = 112/2= 56