Answer:
The number of 20sen and 50sen are 40 and 30
Explanation:
I. The clues we got are total price and total coins,
If 1RM = 100sen
Given b is 50sen and s is 20sen
So 2,300 = 50b + 20s => {total price}
70 = b + s => {total coins}
20* 70 = 20b + 20s => {simulate}
II. Find b or s value by eliminate one of them
{total price} - {simulate}
2,300 - 1,400 = 50b - 20b + 20s - 20s
900 = 30b
b = 30
III. Find s value by replace b value in {total coins}
70 = 30 + s
40 = s
IV. Prove by replace b and s value in {total price}
2,300 = 50(30) + 20(40)
2,300 = 1500 + 800
2,300 = 2,300 true
That makes 40 coins of 20sen and 30 coins of 50sen.
Hope that help :)