Wednesday, April 4, 2012

P5 Maths - Numbers ( Going Backwards Method )

A, B & C has 204 erasers altogether. A gave some to B and B’s erasers doubled. B gave some to C and C’s erasers doubled. In the end, they have equal number of erasers. How many does A have at first?

For this qn, we have to use the “ Going Backwards” method. We have to start from the end, and move backwards step by step.

204 / 3 = 68 (A,B,C has the same at the end)

68 / 2 = 34 ( This is C before his erasers doubled)

68 + 34 = 102 ( This is B before he gave C some eraser)

102 / 2 = 51 (This is B before his erasers doubled)

68 + 51 = 119 ( This is A before he gave B some eraser)

Ans: 119

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