Question 1173937
the formula is M = .8 * (220 - A).
M is the target heart rate.
A is the age of the person.


when M = 156, the formula becomes 156 = .8 * (220 - A).
simplify this formula to get 156 = 176 - .8 * A.
subtract 156 from both sides of this equation and add .8 * A to both sides of this equation to get .8 * A = 176 - 156
combine like terms to get .8 * A = 20
solve for A to get A = 20 / .8 = 25


confirm by replacing A in the original equation to get:
M = .8 * (220 - 25) = .8 * 195 = 156.
this confirms the solution is correct.


the solution is that the age of the person whose target rate is 156 = 25.