Mathematics for IGCSE & O level - Ratio And Proportion (Section 5 - No. 46)
If 4 books cost $36, which statement(s) is/are correct?
The cost of 1 book is $9.
The cost of 8 books is $72.
The cost of 2 books is $24.
The cost of 10 books is $90.
Forklaring
Cost of 1 book = $36/4 = $9. Thus 8 books cost $9*8 = $72. and 10 books cost $9*10 = $90.