Banknotes 7389

My mother had CZK 1,550 in her wallet in CZK 100 and CZK 50 banknotes for 21 pieces. How many banknotes were there?

Correct answer:

a =  10
b =  11

Step-by-step explanation:


1550=100a+50b
21 = a+b

1550=100·a+50·b
21 = a+b

100a+50b = 1550
a+b = 21

Row 2 - 1/100 · Row 1 → Row 2
100a+50b = 1550
0.5b = 5.5


b = 5.5/0.5 = 11
a = 1550-50b/100 = 1550-50 · 11/100 = 10

a = 10
b = 11

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