Răspuns:
d) 5
Explicație pas cu pas:
( 80 + a ) × 5 + 10 = 4 × 100 + ( 9 × 4 - 1 )
( 80 + a ) × 5 + 10 = 400 + ( 36 - 1 )
( 80 + a ) × 5 + 10 = 400 + 35
( 80 + a ) × 5 + 10 = 435
( 80 + a) × 5 = 435 - 10
( 80 + a ) × 5 = 425
80 + a = 425 : 5
80 + a = 85
a = 85 - 80
a = 5
Verificare:
( 80 + 5 ) × 5 + 10 = 4 × 100 + ( 9 × 4 - 1)
85 × 5 + 10 = 400 + 35
425 + 10 = 435
435 = 435