How much does one loaf of bread cost?

One loaf of bread and six rolls cost $1.80. At the same prices, two loaves of bread and four rolls cost $2.40. How much does one loaf of bread cost?

Let B represent the cost of one loaf of bread and R represent the cost of one roll.

1B+6R=$1.80 = 180 cents ------(1)
2B+4R=$2.40 = 240 cents ------(2)

(1) * 2 gives
2B+12R=360 ----(3)

(3)-(2) gives
12R-4R=360-240
8R=120
R=15

B=180-6R=180-6*15=180-90=90

One loaf of bread costs 90 cents.

Who had the least amount of money, and how much was it?

When Anne, Betty and Cynthia compared the amount of money each had they discovered that Anne and Betty together had $12, Betty and Cynthia together had $18, and Anne and Cynthia together had $10. Who had the least amount of money, and how much was it?

Let A, B and C represent the amount of money and Anne, Betty and Cynthia has.

A+B = 12
B+C = 18
A+C = 10

As A+B and A+C is less than B + C => Anne has the least amount of money.

Adding all three equations, A+B+B+C+A+C = 12+18+10 = 40
2A+2B+2C = 40
A+B+C = 20
Substituting B+C = 18
A+18 = 20
A = 2

Anne has $2.

Anne has the least amount of money and she has $2.

How many coins do I have?

I have pennies, quarters, dimes in my piggy bank. If the total number of coins is 4 and the total value is 61¢. How many of each coin do I have?

As its mentioned I have pennies, quarters and dimes.. there should be one of each.
i.e; 1+25+10 = 36¢ and number of coins is 3
Remaining is 61-36=25¢ and there can be only one coin. 
So the last coin should be a quarter.

I have 1 penny, 2 quarters and 1 dime.