PSLE
Ryan had 10 jars of marbles. At first, each of the jars contained the same number of marbles. He took 20 marbles from each jar. After that, the total number of marbles left in the 10 jars was equal to the total number of marbles in 2 of the jars at first. What was the number of marbles in each jar at first?

	2 jars at first	Total jars in the end
Number	2	10
Value	1 u + 20	1 u
Total value	2 u + 40	10 u

Number of marbles in each jar in the end = 1 u
Number of marbles in each jar at first = 1 u + 20

Number of marbles in 2 jars at first 
= 2 x (1 u + 20)
= 2 u + 40

Total number of marbles left in the 10 jars was equal to total number of marbles in 2 jars at first.

10 u = 2 u + 40 
10 u - 2 u = 40
8 u = 40

1 u = 40 ÷ 8 = 5

Number of marbles in each jar at first
= 1 u + 20
= 5 + 20
= 25

Answer(s): 25