Cathy and Gabby collected postcards. Cathy gave 30% of her postcards to Gabby and as a result, Gabby's postcards increased by 10%. If Cathy had 70 postcards left, find the number of postcards Gabby should give to Cathy in the end so that both had an equal number of postcards.

	Cathy	Gabby	Comparing the change in Gabby's postcards
Before	10x1 = 10 u		10x3 = 30u
Change	- 3x1 = - 3 u	+ 3x1 = + 3 u	+ 1x3 = + 3 u
After	7x1 = 7 u		11x3 = 33 u

30% = ³⁰₁₀₀ = ³₁₀
10% = ¹⁰₁₀₀ = ¹₁₀

The increase in the number of postcards that Gabby had is repeated.  Make the increase in the number of postcards that Gabby had the same. LCM of 3 and 1 = 3

7 u = 70

1 u = 70 ÷ 7 = 10

Number of postcards that Gabby had more than Cathy in the end
= 33 u - 7 u
= 26 u

Number of postcards that Gabby should give to Cathy so that both had an equal number of postcards in the end
= 26 u ÷ 2
= 13 u
= 13 x 10
= 130

Answer(s): 130