First, we can find how many cents there are in $10. 10 dollars x 100 cents per dollar = 1000. Then, we divide 1000 by 70 which is equal to 14.29, which rounds to 14. So, Jessica can buy 14 pencils.
To find how much is left we multiply 14 x .70 which gets $9.80. $10 - 9.80 = .20, so she will have 20 cents left over.
Hope I helped!
