Question

Karthik spent 35 dollars of his allowence and 5 dollars on charity. If the number of dollars he spent is porportional to the number of dollars he gives to charity, how much of a 100 dollar allowence will he give to charity?

Answer 1

amount he spent: $40
ratio spent to amount given to charity: 8:1
you can equate fractions

40/5 = 100/x
cross multiply
40x = 500
x = 12.5