An investor received $1400 per annun from a sum of money, with part of it invested at 10% and the remainder at 7% interest. This investor found that if she interchanged the amounts she had invested she could increase her return by $90 per annun. Calculate the total amount invested.
A shopkeeper sold his entire stock of shirts and ties in a sale for $10 000. The hirts were priced at 3 for $100 and the ties $20 each. If he had sold only half the shirts and two-thirds of the ties he would have $6000. How many of each did he sell?
Any help would be appreciated. I would also like to know how to figure these out step by steps.
Thank you for reading.