Question

if the height of a triangle is decreased by 40% and its base is increased by 40%, what will be the percentage change in its area?

Answer 1

0 percent its area will remains. same because the 40 percent which is decreases goes to the base and base increases

Answer 2

I solved this by successive Percentage change formula. 

Formula Used

If a certain number changes successively by A% and B%, the effective percentage change = A+B+AB100" role="presentation" style="display: inline; font-style: normal; font-weight: 400; line-height: normal; font-size: 14px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: 0px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; color: rgb(0, 0, 0); font-family: "Open Sans", sans-serif; font-variant-ligatures: normal; font-variant-caps: normal; orphans: 2; widows: 2; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; position: relative;">A+B+AB100A+B+AB100

In this case, Effective percentage change = 40−40+(40∗−40)100" role="presentation" style="display: inline; font-style: normal; font-weight: 400; line-height: normal; font-size: 14px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: 0px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; color: rgb(0, 0, 0); font-family: "Open Sans", sans-serif; font-variant-ligatures: normal; font-variant-caps: normal; orphans: 2; widows: 2; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial; position: relative;">40−40+(40∗−40)10040−40+(40∗−40)100

= -16 %

Hence the Area of the new triangle decreases by 16%.