Agroup of 10 friends had lunch together at a restaurant. the meal cost a total of $99.50, including a 15% tip. how much was the total bill for lunch before the tip?

Cost of meal before tip + 15% = $99.50

Adding 15% is equal to multiplying by 1.15

Cost of meal before tip x 1.15 = 99.5

This can be rearranged to give;

Cost of meal before tip           = 

Cost of meal before tip          = $86.52

The answer would be 13.5 minutes.