Jack earned $6,400 per month. He spends 30% for his mortgage, 20% to his food and saves the remaining. If he wants to increase his monthly savings by 10% the following month without decrease to the amount given to his food,

(a) How much should he spend for mortgage each month?

$ .00

(b) What’s his difference of monthly mortgage after his changing?

$ .00

(a) The spending for mortgage: 6400 × 30% = 1920

The money for food: 6400 × 20% = 1280

The saving: 6400 – 1920 – 1280 = 3200

Then, the new saving: 3200 × (100% + 10%) = 3520

Thus, the new spending on his mortgage: 6400 – 3520 – 1280 = $1600

(b) The difference: 1920 – 1600 = $320